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U.S. Government Select Portfolio–Siebert Williams shank Shares

U.S. Government Select Portfolio

INVESTMENT OBJECTIVE

The Portfolio seeks to maximize current income to the extent consistent with the preservation of capital and maintenance of liquidity by investing exclusively in high quality money market instruments.

FEES AND EXPENSES of The Portfolio

This table describes the fees and expenses that you may pay if you buy and hold Siebert Williams Shank Shares (formerly, Williams Capital Shares) of the Portfolio.

Shareholder Fees (fees paid directly from your investment)

None

Annual Portfolio Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

	Siebert Williams Shank Shares
Management Fees	0.18%
Other Expenses	0.03%
Transfer Agent Fees	0.02%
Service Fees	None
Other Operating Expenses	0.01%
Total Annual Portfolio Operating Expenses	0.21%
Expense Reimbursement(1)	(0.01)%
Total Annual Portfolio Operating Expenses After Expense Reimbursement(2)	0.20%

(1)

Northern Trust Investments, Inc. (“NTI”) has contractually agreed to reimburse a portion of the operating expenses of the Portfolio (other than certain excepted expenses, i.e., Acquired Fund Fees and Expenses, service fees, the compensation paid to each Independent Trustee of the Trust, expenses of third party consultants engaged by the Board of Trustees, membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum, expenses in connection with the negotiation and renewal of the revolving credit facility, extraordinary expenses and interest) to the extent the “Total Annual Portfolio Operating Expenses” exceed 0.20%. This contractual limitation may not be terminated before April 1, 2022 without the approval of the Board of Trustees.

(2)

The Total Annual Portfolio Operating Expenses After Expense Reimbursement will not correlate to the Portfolio’s ratio of average net assets to expenses, net of waivers, reimbursements and credits included in the Portfolio’s Financial Highlights in the Portfolio’s complete Prospectus, which reflect voluntarily expense reimbursements made by NTI to the Portfolio.

EXAMPLE

The following Example is intended to help you compare the cost of investing in Siebert Williams Shank Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment

has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

	1 Year	3 Years	5 Years	10 Years
Siebert Williams Shank Shares	$20	$67	$117	$267

PRINCIPAL INVESTMENT STRATEGIES

The Portfolio seeks to achieve its objective by investing, under normal circumstances, substantially all (and at least 99.5%) of its total assets in cash, securities issued or guaranteed as to principal and interest by the U.S. government or by a person controlled or supervised by and acting as an instrumentality of the U.S. government pursuant to authority granted by the Congress of the United States or any certificate of deposit of any of the foregoing, and repurchase agreements that are fully collateralized by cash or such securities. Subject to the foregoing 99.5% investment strategy requirement, under normal circumstances, the Portfolio will seek to invest at least 50% of its net assets in the following securities that pay interest that generally is exempt from state income taxation:

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U.S. Treasury bills;

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U.S. Treasury notes;

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U.S. Treasury STRIPS;

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securities issued by the Federal Home Loan Bank (FHLB);

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securities issued by the Federal Farm Credit Bank (FFCB); and

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securities issued by the Tennessee Valley Authority.

The Portfolio, under normal circumstances, will invest at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in U.S. government securities and repurchase agreements collateralized solely by U.S. government securities.

The Portfolio operates as a “government money market fund” under Rule 2a-7 of the Investment Company Act of 1940, as amended. As a “government money market fund” under Rule 2a-7, the Portfolio (1) is permitted to use the amortized cost method of valuation to seek to maintain a stable net asset value (“NAV”) of $1.00 share price, and (2) is not required to impose a liquidity fee and/or a redemption gate on Portfolio redemptions that might apply to other types of money market funds should certain triggering events specified in Rule 2a-7 occur.

The Securities and Exchange Commission (“SEC”) imposes strict requirements on the investment quality, maturity, diversification and liquidity of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s

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investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio.

PRINCIPAL RISKS

As with any investment, you could lose all or part of your investment in the Portfolio, and the Portfolio’s performance could trail that of other investments. The Portfolio is subject to certain risks, including the principal risks noted below, any of which may adversely affect the Portfolio’s NAV, trading price, yield, total return and ability to meet its investment objective. Each risk noted below is considered a principal risk of investing in the Portfolio, regardless of the order in which it appears. The significance of each risk factor below may change over time and you should review each risk factor carefully.

STABLE NAV RISK is the risk that the Portfolio will not be able to maintain a NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share. If the Portfolio fails to maintain a stable NAV (or if there is a perceived threat of such a failure), the Portfolio could be subject to increased redemption activity, which could adversely affect its NAV.

INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher. Securities with longer maturities tend to be more sensitive to changes in interest rates, causing them to be more volatile than securities with shorter maturities. Securities with shorter maturities tend to provide lower returns and be less volatile than securities with longer maturities. If interest rates rise, the Portfolio’s yield may not increase proportionately, and the maturities of income securities that have the ability to be prepaid or called by the

issuer may be extended. Interest rates in the U.S. are currently at historically low levels. Changing interest rates may have unpredictable effects on the markets and the Portfolio’s investments. A low or negative interest rate environment could cause the Portfolio’s earnings to fall below the Portfolio’s expense ratio, resulting in a low or negative yield and a decline in the Portfolio’s share price. A general rise in interest rates may cause investors to move out of fixed income securities on a large scale, which could adversely affect the price and liquidity of fixed income securities and could also result in increased redemptions for the Portfolio. Fluctuations in interest rates may also affect the liquidity of fixed income securities and instruments held by the Portfolio.

CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its principal or interest payments or other financial obligations will adversely affect the value of the Portfolio’s investments and its returns. The credit quality of a debt security or of the issuer of a debt security held by the Portfolio could deteriorate rapidly, which may impair the Portfolio’s liquidity or cause a deterioration in the Portfolio’s NAV. The Portfolio could also be delayed or hindered in its enforcement of rights against an issuer, guarantor or counterparty.

DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities.

PREPAYMENT (OR CALL) RISK is the risk that because many issuers of fixed-income securities have an option to prepay their fixed-income securities, the exercise of such option may result in a decreased rate of return and a decline in value of those securities and accordingly, a decline in the Portfolio’s NAV. Issuers may be more likely to prepay their securities if interest rates fall. If this happens, the Portfolio will not benefit from the rise in the market price of the securities that normally accompanies a decline in interest rates, and will be forced to reinvest prepayment proceeds at a time when yield on securities available in the market are lower than the yield on prepaid securities. The Portfolio may also lose any premium it paid to purchase the securities.

VARIABLE OR FLOATING RATE INSTRUMENTS RISK is the risk that securities with variable or floating rates can be less sensitive to interest rate changes than securities with fixed interest rates, but may decline in value and negatively impact the Portfolio, particularly if changes in prevailing interest rates are more frequent or sudden than the rate changes for the variable or floating rate securities, which only occur periodically. Although variable and floating rate securities are less sensitive to interest rate risk than fixed-rate securities, they are subject to greater liquidity risk, credit risk and default risk, which could impede their value.

INCOME RISK is the risk that the Portfolio’s ability to distribute income to shareholders depends on the yield available from the Portfolio’s investments. Falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities.

U.S. GOVERNMENT SECURITIES RISK is the risk that the U.S. government will not provide financial support to its agencies, instrumentalities or sponsored enterprises if it is not obligated to do so by law. Certain U.S. government securities purchased by the Portfolio are neither issued nor guaranteed by the U.S. Treasury and, therefore, may not be backed by the full faith and

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credit of the United States. The maximum potential liability of the issuers of some U.S. government securities may greatly exceed their current resources, including any legal right to support from the U.S. Treasury. It is possible that the issuers of such securities will not have the funds to meet their payment obligations in the future.

MARKET RISK is the risk that the value of the Portfolio’s investments may increase or decrease in response to expected, real or perceived economic, political or financial events in the U.S. or global markets. The frequency and magnitude of such changes in value cannot be predicted. Certain securities and other investments held by the Portfolio may experience increased volatility, illiquidity, or other potentially adverse effects in response to changing market conditions, inflation, changes in interest rates, lack of liquidity in the bond or equity markets, volatility in the equity markets, market disruptions caused by local or regional events such as war, acts of terrorism, the spread of infectious illness (including epidemics and pandemics) or other public health issues, recessions or other events or adverse investor sentiment or other political, regulatory, economic and social developments, and developments that impact specific economic sectors, industries or segments of the market. These risks may be magnified if certain events or developments adversely interrupt the global supply chain; in these and other circumstances, such risks might affect companies worldwide due to increasingly interconnected global economies and financial markets.

MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results or that imperfections, errors or limitations in the tools and data used by the investment adviser may cause unintended results.

CYBERSECURITY RISK is the risk of an unauthorized breach and access to Portfolio assets, Portfolio or customer data (including private shareholder information), or proprietary information, or the risk of an incident occurring that causes the Portfolio, the investment adviser, custodian, transfer agent, distributor and other service providers and financial intermediaries to suffer data breaches, data corruption or lose operational functionality or prevent Portfolio investors from purchasing, redeeming or exchanging shares or receiving distributions. The Portfolio and its investment adviser have limited ability to prevent or mitigate cybersecurity incidents affecting third party service providers, and such third-party service providers may have limited indemnification obligations to the Portfolio or its investment adviser. Successful cyber-attacks or other cyber-failures or events affecting the Portfolio or its service providers may adversely impact and cause financial losses to the Portfolio or its shareholders. Issuers of securities in which the Portfolio invests are also subject to cybersecurity risks, and the value of these securities could decline if the issuers experience cyber-attacks or other cyber-failures.

LARGE SHAREHOLDER RISK is the risk that the Portfolio may experience adverse effects when certain large shareholders, including funds or accounts over which the Portfolio’s investment adviser or an affiliate of the investment adviser has investment discretion, purchase or redeem large amounts of shares of the Portfolio. Such large shareholder redemptions, which may occur rapidly and unexpectedly, may cause the Portfolio to sell its securities at times it would not otherwise do so, which may negatively impact its liquidity and/or NAV. Such sales may also accelerate the realization of taxable income to shareholders if these sales result in gains, and may also increase transaction costs. In addition, large redemptions could lead to an increase in the Portfolio’s expense ratio due to expenses being allocated over a smaller asset base. Large purchases of the Portfolio’s shares may also adversely affect the Portfolio’s performance to the extent that the Portfolio is delayed in investing new cash or otherwise maintains a larger cash position than it ordinarily would.

You could lose money by investing in the Portfolio. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, the Portfolio cannot guarantee it will do so. An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, Siebert Williams Shank & Co., LLC or its affiliates, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. The Portfolio’s sponsor has no legal obligation to provide financial support to the Portfolio, and you should not expect that the sponsor will provide financial support to the Portfolio at any time.

PORTFOLIO PERFORMANCE

The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio from year to year.

The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.

Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s website at northerntrust.com/institutional or by calling 800-637-1380.

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U.S. Government Select Portfolio–Siebert Williams shank Shares

U.S. Government Select Portfolio

CALENDAR YEAR TOTAL RETURNS (SHARES)*

For the periods shown in the bar chart above:

highest quarterly return	0.56%	second quarter of 2019
lowest quarterly return	0.00%	third quarter of 2015

AVERAGE ANNUAL TOTAL RETURNS

(For the periods ended December 31, 2020)

	Inception Date	1 Year	5 Years	Since Inception
Siebert Williams Shank Shares	09/15/2014	0.40%	1.02%	0.81%

The 7-day yield for Siebert Williams Shank Shares of the Portfolio as of December 31, 2020: 0.02%. For the current 7-day yield call 800-637-1380 or visit northerntrust.com/institutional.

MANAGEMENT

INVESTMENT ADVISER. Northern Trust Investments, Inc. (“NTI”), an indirect subsidiary of Northern Trust Corporation, serves as the investment adviser of the Portfolio. The Northern Trust Company, an affiliate of NTI, serves as transfer agent, custodian and sub-administrator to the Portfolio.

PURCHASE AND SALE OF PORTFOLIO SHARES

You may purchase Siebert Williams Shank Shares of the Portfolio through an account directly with the Northern Institutional Funds, through your institutional account at Northern Trust (or an affiliate) or through an authorized intermediary, generally with no minimum initial investment.

On any business day, you may sell (redeem) or exchange Siebert Williams Shank Shares of the Portfolio through your institutional account by contacting your Northern Trust account representative or authorized intermediary. If you purchase Siebert Williams Shank Shares of the Portfolio directly from the Trust, you may sell (redeem) or exchange your shares in one of the following ways:

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By Mail – Send a written request to: Northern Institutional Funds, P.O. Box 75986, Chicago, Illinois 60675-5986.

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By Telephone – Call the Northern Institutional Funds Center at 800-637-1380.

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By Wire – Authorize wire redemptions on your New Account Application and have proceeds sent by federal wire transfer to a previously designated bank account (the minimum redemption amount by this method is $10,000).

TAX INFORMATION

The Portfolio’s distributions are generally taxable to you as ordinary income, capital gains, or a combination of the two, unless you are investing through a tax-exempt or tax-deferred arrangement, such as a 401(k) plan or an individual retirement account. Distributions may be taxable upon withdrawal from tax-deferred accounts.

PAYMENTS TO BROKERS-DEALERS AND OTHER FINANCIAL INTERMEDIARIES

If you purchase Siebert Williams Shank Shares of the Portfolio through a broker-dealer or other financial intermediary (such as a bank), the Portfolio and its related companies may pay the intermediary for the sale of Siebert Williams Shank Shares of the Portfolio and related services. These payments may create a conflict of interest by influencing the broker-dealer or other intermediary and your salesperson to recommend the Portfolio over another investment. Ask your salesperson or visit your financial intermediary’s website for more information.

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U.S. Government Select Portfolio–Siebert Williams shank Shares

Investment Adviser

This Prospectus describes one money market portfolio (the “Portfolio”), which is currently offered by Northern Institutional Funds (the “Trust”).

Northern Trust Investments, Inc. (“NTI” or the “Investment Adviser”), an indirect subsidiary of Northern Trust Corporation, serves as the Investment Adviser of the Portfolio and is responsible for its overall administration. NTI is located at 50 South LaSalle Street, Chicago, Illinois 60603.

NTI is an Illinois State Banking Corporation and an investment adviser registered under the Investment Advisers Act of 1940, as amended. It primarily manages assets for institutional and individual separately managed accounts, investment companies and bank common and collective funds.

Northern Trust Corporation is regulated by the Board of Governors of the Federal Reserve System as a financial holding company under the U.S. Bank Holding Company Act of 1956, as amended. Unless otherwise indicated, NTI and The Northern Trust Company (“TNTC”) are referred to collectively in this Prospectus as “Northern Trust.”

As of December 31, 2020, Northern Trust Corporation, through its affiliates, had assets under custody of $11.26 trillion and assets under investment management of $1.4 trillion.

Under the Management Agreement with the Trust, the Investment Adviser, subject to the general supervision of the Trust’s Board of Trustees, is responsible for making investment decisions for the Portfolio and for placing purchase and sale orders for portfolio securities, as well as for providing administration services to the Portfolio.

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Management Fees

As compensation for advisory services and administration services and the assumption of related expenses, NTI is entitled to a management fee, computed daily and payable monthly, at annual rates set forth in the table below (expressed as a percentage of the Portfolio’s average daily net assets). The table also reflects the management fees paid by the Portfolio for the fiscal year ended November 30, 2020 (expressed as a percentage of the Portfolio’s average daily net assets).

NTI has contractually agreed to reimburse a portion of the operating expenses of the Portfolio (other than certain fees and expenses shown in the table under the caption “Fees and Expenses of the Portfolio” in the Portfolio’s Portfolio Summary) so that “Total Annual Portfolio Operating Expenses After Expense Reimbursement” do not exceed the amount shown in the footnote to the table under the caption “Fees and Expenses of the Portfolio” in the Portfolio Summary. The “Total Annual Portfolio Operating Expenses After Expense Reimbursement” for the Portfolio may be higher than the contractual limitation for the Portfolio as a result of certain excepted expenses that are not reimbursed. The contractual expense reimbursement

arrangement is expected to continue until at least April 1, 2022. The contractual expense reimbursement arrangement will continue automatically thereafter for periods of one year (each such one-year period, a “Renewal Year”). The arrangement may be terminated, as to any succeeding Renewal Year, by NTI or the Portfolio upon 60 days’ written notice prior to the end of the current Renewal Year. The Board of Trustees may terminate the arrangement at any time if it determines that it is in the best interest of the Portfolio and its shareholders.

NTI may reimburse additional expenses or waive all or a portion of the management fees of the Portfolio from time to time, including to avoid a negative yield. Any such additional expense reimbursement or fee waiver would be voluntary and could be implemented, increased or decreased, or discontinued at any time. There is no guarantee that the Portfolio will be able to avoid a negative yield.

A discussion regarding the Board of Trustees’ basis for its most recent approval of the Portfolio’s Management Agreement is available in the Portfolio’s semi-annual report to shareholders for the six-month period ended May 31, 2020.

	Contractual Management Fee Rate	Management Fees Paid for Fiscal Year Ended 11/30/2020
U.S. GOVERNMENT SELECT PORTFOLIO	0.18%	0.18%

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OTHER PORTFOLIO SERVICES

TNTC serves as Transfer Agent and Custodian for the Portfolio. The Transfer Agent performs various shareholder servicing functions, and any shareholder inquiries should be directed to it. TNTC also performs certain administrative services for the Portfolio pursuant to a sub-administration agreement with NTI. NTI pays TNTC for its sub-administration services out of its management fees, which do not represent additional expenses to the Portfolio.

TNTC, as Transfer Agent, is entitled to transfer agent fees at an annual rate of 0.015% of the average daily net assets of the Portfolio. TNTC, as Custodian, receives an amount based on a pre-determined schedule of charges approved by the Trust’s

Board of Trustees. TNTC, NTI and other Northern Trust affiliates may provide other services to the Portfolio and receive compensation for such services if consistent with the Investment Company Act of 1940, as amended (the “1940 Act”) and the rules, exemptive orders and no-action letters issued by the SEC thereunder. Unless required, investors in the Portfolio may or may not receive specific notice of such additional services and fees.

Shares of the Trust are distributed by Northern Funds Distributors, LLC (“NFD”), Three Canal Plaza, Suite 100, Portland, Maine, 04101. NFD is not affiliated with TNTC, NTI or any other Northern Trust affiliate.

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PURCHASING AND SELLING siebert WILLIAMS shank SHARES

THE TRUST OFFERS one MONEY MARKET PORTFOLIO TO INSTITUTIONAL INVESTORS IN THIS PROSPECTUS

The description in the Portfolio Summary may help you decide whether the Portfolio fits your investment needs. Keep in mind, however, that no guarantee can be made that the Portfolio will meet its investment objective and the Portfolio should not be relied upon as a complete investment program.

SHARE CLASSES

The Portfolio is authorized to offer four classes of shares (Shares, Service Shares, Premier Shares and Siebert Williams Shank Shares). Shares, Service Shares and Premier Shares are described in separate prospectuses.

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Siebert Williams Shank Shares bear their pro rata portion of all operating expenses paid by the Portfolio, except for transfer agent fees.

Please note that the fee and expense information shown under “Fees and Expenses of the Portfolio” in the Portfolio Summary beginning on page 3 does not reflect any charges (such as allocation or account maintenance fees) that may be imposed by TNTC, its affiliates, Siebert Williams Shank & Co., LLC (“SWS”) or other financial intermediaries on their clients. SWS is a minority- and women-owned independent, non-bank financial services firm. SWS is not affiliated with Northern Trust. (For more information, please see “Account Policies and Other Information—Financial Intermediaries” on page 15.)

PURCHASING Siebert Williams Shank SHARES

OPENING AN ACCOUNT

THROUGH AN INSTITUTIONAL ACCOUNT. If you are opening an institutional account at Northern Trust, a Northern Trust representative can assist you with all phases of your investment. To purchase shares through your account, contact your Northern Trust representative for further information.

THROUGH AN AUTHORIZED INTERMEDIARY. The Trust has authorized certain Institutions acting as financial intermediaries (including banks, trust companies, brokers and investment advisers) to accept purchase orders from their customers on behalf of the Portfolio. See “Account Policies and Other

Information—Financial Intermediaries” beginning on page 15 for additional information regarding purchases of Siebert Williams Shank Shares of the Portfolio through authorized intermediaries.

DIRECTLY FROM THE TRUST. Investors may open a shareholder account and purchase shares directly from the Trust as described above under “Purchasing Shares”.

For your convenience, there are a number of ways to invest directly in the Portfolio:

BY MAIL

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Read this Prospectus carefully.

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Complete and sign the New Account Application.

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Include acceptable evidence of authority (if applicable).

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Enclose a check or Federal Reserve draft payable to Northern Institutional Funds.

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Mail your check, acceptable evidence of authority (if applicable) and completed New Account Application to:

Northern Institutional Funds
P.O. Box 75986
Chicago, Illinois 60675-5986

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Additional documentation may be required to fulfill the requirements of the “Customer Identification Program” described beginning on page 14.

All checks must be payable in U.S. dollars and drawn on a bank located in the United States. Cash and third party checks are not acceptable.

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For overnight delivery, use the following address:

Northern Institutional Funds
c/o The Northern Trust Company
333 South Wabash Ave
Chicago, Illinois 60604

BY TELEPHONE

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Read this Prospectus carefully.

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Call the Northern Institutional Funds Center at 800-637-1380.

TO OPEN A NEW ACCOUNT PLEASE PROVIDE:

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The name of the Portfolio in which you would like to invest

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The number of shares or dollar amount to be invested

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The method of payment

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TO ADD TO AN EXISTING ACCOUNT, PLEASE PROVIDE:

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The Institution’s name

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Your account number

BY WIRE OR AUTOMATED CLEARING HOUSE (“ACH”) TRANSFER

TO OPEN A NEW ACCOUNT:

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For more information or instructions regarding the purchase of shares, call the Northern Institutional Funds Center at 800-637-1380.

TO ADD TO AN EXISTING ACCOUNT:

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Have your bank wire federal funds or effect an ACH transfer to:

The Northern Trust Company
Chicago, Illinois
ABA Routing No. 0710-00152
(Reference 10-Digit Portfolio account number, with no spaces
(e.g., ##########))
(Reference Shareholder’s Name)

SELLING Siebert Williams Shank SHARES

THROUGH AN INSTITUTIONAL ACCOUNT. You may sell (redeem) shares through your institutional account by contacting your Northern Trust account representative.

THROUGH AN AUTHORIZED INTERMEDIARY. If you purchased shares from an authorized intermediary, you may sell (redeem) shares by contacting your financial intermediary. See “Account Policies and Other Information—Financial Intermediaries” on page 15 for additional information regarding sales (redemptions) of Siebert Williams Shank Shares of the Portfolio through authorized intermediaries.

DIRECTLY THROUGH THE TRUST. Purchasers of Siebert Williams Shank Shares that purchase shares directly from the Trust may redeem their shares through the Transfer Agent in one of the following ways:

BY MAIL

SEND A WRITTEN REQUEST TO:

Northern Institutional Funds
P.O. Box 75986
Chicago, Illinois 60675-5986

THE LETTER OF INSTRUCTION MUST INCLUDE:

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The signature of a duly authorized person (A signature guarantee from an institution participating in the Stock Transfer Agency Medallion Program (“STAMP”) also may be required.)

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Your account number

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The name of the Portfolio

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The number of shares or the dollar amount to be redeemed

BY TELEPHONE

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Call the Northern Institutional Funds Center at 800-637-1380 for instructions.

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During periods of unusual economic or market activity, telephone redemptions may be difficult to implement. In such event, shareholders should follow the procedures outlined above under “Selling Siebert Williams Shank Shares—By Mail.”

BY WIRE

If you authorize wire redemptions on your New Account Application, you can redeem shares and have the proceeds sent by federal wire transfer to a previously designated bank account.

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Call the Northern Institutional Funds Center at 800-637-1380 for instructions.

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The minimum amount that may be redeemed by this method is $10,000.

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ACCOUNT POLICIES AND OTHER INFORMATION

PURCHASE AND REDEMPTION MINIMUMS. There is generally no minimum initial investment for Siebert Williams Shank Shares of the Portfolio when purchasing shares through an authorized intermediary. A $10,000 minimum applies for redemptions by wire. The Trust reserves the right to waive redemption minimums and to determine the manner in which a minimum is satisfied.

CALCULATING SHARE PRICE. The Trust issues and redeems Siebert Williams Shank Shares at NAV. The NAV for Siebert Williams Shank Shares of the Portfolio is calculated by dividing the value of the Portfolio’s net assets attributed to Siebert Williams Shank Shares by the number of the Portfolio’s outstanding Siebert Williams Shank Shares. The NAV for the Portfolio is calculated on each Business Day as of 4:00 p.m. Central time. Portfolio shares may be priced on days when the New York Stock Exchange (the “Exchange”) is closed if the Securities Industry and Financial Markets Association (“SIFMA”) recommends that the bond markets remain open for all or part of the day or on days when the Federal Reserve Bank of New York (the “New York Fed”) is open. The NAV used in determining the price of your shares is the one calculated after your purchase, exchange or redemption order is received in good order as described on page 14.

The Portfolio seeks to maintain a stable NAV of $1.00 per share by valuing the obligations held by it at amortized cost in accordance with SEC regulations. Amortized cost will normally approximate fair value.

TIMING OF PURCHASE REQUESTS. Purchase requests received in good order and accepted by the Transfer Agent or other authorized intermediary on any Business Day by 4:00 p.m. Central time, will be executed the day they are received by either the Transfer Agent or other authorized intermediary at that day’s closing share price for the Portfolio, provided that one of the following occurs:

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The Transfer Agent receives the payment in federal or other immediately available funds on the same Business Day by the close of the Federal Reserve wire transfer system (normally, 5:00 p.m. Central time);

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The requests are placed by a financial or authorized intermediary that has entered into a servicing agreement or other agreement with the Trust or its agent and payment in federal or other immediately available funds is received by the Transfer Agent by the close of the same Business Day in accordance with the terms of the Trust’s or its agent’s agreement with the intermediary;

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Payment in federal or other immediately available funds is received by the close of the same Business Day in an institutional account maintained with Northern Trust or an affiliate; or

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The purchase requests are placed through TNTC’s electronic fund trading platform and payment in federal or other immediately available funds is received by the Transfer Agent by the close of the Federal Reserve wire transfer system (normally, 5:00 p.m. Central time).

Purchase requests received in good order by the Transfer Agent or other authorized intermediary on a non-Business Day or after the deadlines described above on a Business Day will be executed on the next Business Day, at that day’s closing share price for the Portfolio, provided that payment is made as noted above.

IN-KIND PURCHASES AND REDEMPTIONS. The Trust reserves the right to accept payment for Siebert Williams Shank Shares in the form of securities that are permissible investments for the Portfolio. The Trust also reserves the right to pay redemptions by a distribution “in-kind” of securities (instead of cash) from the Portfolio. See the SAI for further information about the terms of these purchases and redemptions.

MISCELLANEOUS PURCHASE INFORMATION.

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Purchasers of Siebert Williams Shank Shares are responsible for transmitting purchase orders and delivering required funds on a timely basis.

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Holders of Siebert Williams Shank Shares are responsible for all losses and expenses of the Portfolio, and purchase orders may be cancelled, in the event of any failure to make payment according to the procedures outlined in this Prospectus. In addition, a $20 charge will be imposed if a check does not clear.

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Exchanges into the Portfolio from another investment portfolio in the Trust may be subject to any redemption fee imposed by the other investment portfolio.

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Siebert Williams Shank Shares of the Portfolio are entitled to the dividends declared by the Portfolio beginning on the Business Day the purchase order is executed, provided payment in federal or other immediately available funds is received by the Transfer Agent by the time designated in “Timing of Purchase Requests” on page 12.

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The Trust, its agents and NFD each reserves the right, in the Trust’s sole discretion, to reject or restrict any purchase order or exchange order, in whole or in part, for any reason. The Trust also reserves the right to change or discontinue any of its purchase procedures.

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The Trust, its agents and NFD each reserves the right to suspend the offering of shares of the Portfolio when, in the judgment of management, such suspension is in the best interests of the Portfolio.

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In certain circumstances, the Trust may advance the time by which purchase orders must be received. See “Early Closings” on page 15.

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If the Transfer Agent cannot locate an investor for a period of time specified by appropriate state law, the investor’s account

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may be deemed legally abandoned and then escheated (transferred) to such state’s unclaimed property administrator in accordance with statutory requirements.

TIMING OF REDEMPTION AND EXCHANGE REQUESTS.Redemption and exchange requests received in good order by the Transfer Agent on any Business Day by 4:00 p.m. Central time, will be executed on the same day at that day’s closing share price for the Portfolio.

Redemption and exchange requests received in good order by the Transfer Agent or other authorized intermediary on a non-Business Day or after the deadline described above on a Business Day will be executed the next Business Day at that day’s closing share price for the Portfolio.

PAYMENT OF REDEMPTION PROCEEDS. If your account is held directly with the Portfolio, it is expected that the Portfolio will typically pay out redemption proceeds to shareholders by the next Business Day following a receipt of a redemption request.

If your account is held through an intermediary, the length of time to pay redemption proceeds typically depends, in part, on the terms of the agreement in place between the intermediary and the Portfolio. For redemption proceeds that are paid either directly to you from the Portfolio or to your intermediary for transmittal to you, it is expected that payments will typically be made by wire, by ACH or by issuing check by the next Business Day following receipt of a redemption request in good order from the intermediary by the Portfolio. Redemption requests that are processed through investment professionals that utilize the National Securities Clearing Corporation will generally settle one to three Business Days following receipt of a redemption request in good order.

However, if you have recently purchased shares with a check or through an electronic transaction, payment may be delayed as discussed below under “Miscellaneous Redemption Information.”

It is expected that payment of redemption proceeds will normally be made from uninvested cash or short-term investments, proceeds from the sale of portfolio securities, or borrowing through the Trust’s committed, unsecured credit facility (see “Credit Facility and Borrowing,” on page 21). It is possible that stressed market conditions or large shareholder redemptions may result in the need for utilization of the Portfolio’s ability to redeem in-kind in order to meet shareholder redemption requests. The Portfolio reserves the right to pay all or part of your redemption proceeds in readily marketable securities instead of cash (redemption in-kind). Redemption in-kind proceeds will typically be made by delivering the selected securities to the redeeming shareholder within seven days after the receipt of the redemption request in good order by the Portfolio.

The Portfolio does not intend to avail itself of the ability to impose liquidity fees and/or redemption gates. However, the Board of Trustees reserves the right, with notice to shareholders, to change this policy, thereby permitting the Portfolio to impose such fees and gates in the future.

MISCELLANEOUS REDEMPTION INFORMATION. All redemption proceeds will be sent by check unless the Transfer Agent is directed otherwise. Redemption proceeds also may be wired. Redemptions are subject to the following restrictions:

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The Trust reserves the right to defer crediting, sending or wiring redemption proceeds for up to 7 days (or such longer period permitted by the SEC) after receiving the redemption order if, in its judgment, an earlier payment could adversely affect the Portfolio. The processing of redemptions may be suspended, and the delivery of redemption proceeds may be delayed beyond seven days, depending on the circumstances, for any period: (i) during which the Exchange is closed (other than on holidays or weekends), or during which trading on the Exchange is restricted; (ii) when an emergency exists that makes the disposal of securities owned by the Portfolio or the determination of the fair value of the Portfolio’s net assets not reasonably practicable; or (iii) as permitted by order of the SEC for the protection of Portfolio shareholders.

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If you are redeeming Siebert Williams Shank Shares recently purchased by check or electronic transaction, your redemption request may not be paid until your check or electronic transaction has cleared. This may delay your payment for up to 10 days.

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Redemption requests made to the Transfer Agent by mail must be signed by a person authorized by acceptable documentation on file with the Transfer Agent.

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Dividends on Siebert Williams Shank Shares are earned through and including the day prior to the day on which they are redeemed.

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Holders of Siebert Williams Shank Shares are responsible for transmitting redemption orders.

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Subject to applicable law, the Trust and the Transfer Agent reserve the right to redeem shares held by any shareholder who provides incorrect or incomplete account information or when such involuntary redemptions are necessary to avoid adverse consequences to the Trust and its shareholders or the Transfer Agent.

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Subject to applicable law, the Trust, Northern Trust and their agents reserve the right to involuntarily redeem or suspend an account at the Portfolio’s then current NAV, in cases of disruptive conduct, suspected fraudulent or illegal activity, inability to verify the identity of an investor, or other circumstances determined by the Trust and Northern Trust to be in the best interest of the Trust and its shareholders.

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The Trust, Northern Trust and their agents reserve the right, without notice, to freeze any account and/or suspend account

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services when: (i) notice has been received of a dispute regarding the assets in an account, or a legal claim against an account; (ii) upon initial notification to Northern Trust of a shareholder’s or authorized agent’s death until Northern Trust receives required documentation in correct form; or (iii) if there is reason to believe a fraudulent transaction may occur or has occurred.

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The Trust may require any information from the shareholder reasonably necessary to ensure that a redemption request has been duly authorized.

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The Trust reserves the right to change or discontinue any of its redemption procedures.

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The Trust does not permit redemption proceeds to be sent by outgoing International ACH Transaction (“IAT”). An IAT is a payment transaction involving a financial institution’s office located outside U.S. territorial jurisdiction.

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In certain circumstances, the Trust may advance the time by which redemption and exchange orders must be received. See “Early Closings” on page 15.

EXCESSIVE TRADING IN PORTFOLIO SHARES. The Board of Trustees of the Trust has not adopted, on behalf of the Portfolio, policies and procedures with respect to frequent purchases and redemptions of Portfolio shares in light of the nature and high quality of the Portfolio’s investments. The Portfolio reserves the right to refuse a purchase order if management of the Portfolio determines that the purchase may not be in the best interests of the Portfolio.

TELEPHONE TRANSACTIONS. All calls may be recorded or monitored. The Transfer Agent has adopted procedures in an effort to establish reasonable safeguards against fraudulent telephone transactions. If reasonable measures are taken to verify that telephone instructions are genuine, the Trust and its service providers will not be responsible for any loss resulting from fraudulent or unauthorized instructions received over the telephone. In these circumstances, shareholders will bear the risk of loss. During periods of unusual market activity, you may have trouble placing a request by telephone. In this event, consider sending your request in writing by following the procedures outlined above under “Purchasing and Selling Siebert Williams Shank Shares—Selling Siebert Williams Shank Shares—By Mail.”

The proceeds of redemption orders received by telephone will be sent by check, wire or transfer according to proper instructions. All checks will be made payable to the shareholder of record and mailed only to the shareholder’s address of record.

The Trust reserves the right to refuse a telephone redemption, subject to applicable law.

ADVANCE NOTIFICATION OF LARGE TRANSACTIONS. The Trust requests that shareholders give advance notice to the Transfer Agent by 11:00 a.m. Central time if they intend to place a purchase or redemption order of $5 million or more on a

Business Day. For other large purchase or redemption orders below $5 million, the Trust requests that a shareholder give advance notice to the Transfer Agent as early as possible in the day.

MAKING CHANGES TO YOUR ACCOUNT INFORMATION. You may make changes to wiring instructions only in writing. You may make changes to an address of record or certain other account information in writing or by telephone. Written instructions must be accompanied by acceptable evidence of authority (if applicable). A signature guarantee also may be required from an institution participating in STAMP. Additional requirements may be imposed. In accordance with SEC regulations, the Trust and Transfer Agent may charge a shareholder reasonable costs in locating a shareholder’s current address.

SIGNATURE GUARANTEES. If a signature guarantee is required, it must be from an institution participating in STAMP, or other acceptable evidence of authority (if applicable) must be provided. Additional requirements may be imposed by the Trust. In addition to the situations described in this Prospectus, the Trust may require signature guarantees in other circumstances based on the amount of a redemption request or other factors.

BUSINESS DAY. A “Business Day” is each Monday through Friday that the New York Fed is open for business, except as noted below. The New York Fed is closed on the following national holidays: New Year’s Day, Martin Luther King, Jr. Day, Presidents’ Day, Memorial Day, Independence Day, Labor Day, Columbus Day, Veterans Day, Thanksgiving Day and Christmas Day. The Portfolio may also close on days when the New York Fed is open but the Exchange is closed, such as Good Friday.

GOOD ORDER. A purchase, redemption or exchange request is considered to be “in good order” when all necessary information is provided and all required documents are properly completed, signed and delivered, including acceptable evidence of authority (if applicable). Additionally, a purchase order initiating the opening of an account will not be considered to be “in good order” unless the investor has provided all information required by the Trust’s “Customer Identification Program” described below.

CUSTOMER IDENTIFICATION PROGRAM. Federal law requires the Trust to obtain, verify and record identifying information, which may include the name, business street address, taxpayer identification number or other identifying information for each investor who opens or reopens an account with the Trust. Applications without this information, or without an indication that a taxpayer identification number has been applied for, may not be accepted. After acceptance, to the extent permitted by applicable law or the Trust’s customer identification program, the Trust reserves the right to: (a) place limits on account transactions until an investor’s identity is verified; (b) refuse an investment in the Trust; or (c) involuntarily redeem an investor’s shares and close an account in the event that an investor’s identity is not verified. The Trust and its agents will not be

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responsible for any loss in an investor’s account resulting from an investor’s delay in providing all required identifying information or from closing an account and redeeming an investor’s shares when an investor’s identity is not verified.

EARLY CLOSINGS. The Portfolio reserves the right to advance the time for accepting purchase, redemption or exchange orders for same Business Day credit when the Exchange and/or the bond market close early, trading on the Exchange is restricted, an emergency arises or as otherwise permitted by the SEC. In addition, on any Business Day when SIFMA recommends that the bond markets close early, the Portfolio reserves the right to close at or prior to the SIFMA recommended closing time. If the Portfolio does so, it will cease granting same Business Day credit for purchase and redemption orders received at the Portfolio’s closing time and credit will be given on the next Business Day. In addition, the Board of Trustees of the Trust also may, for any Business Day, decide to change the time as of which the Portfolio’s NAV is calculated in response to new developments such as altered trading hours, or as otherwise permitted by the SEC.

EMERGENCY OR UNUSUAL EVENTS. In the event the Exchange does not open for business because of an emergency or unusual event, the Trust may, but is not required to, open one or more Portfolios for purchase, redemption and exchange transactions if the Federal Reserve wire payment system is open. To learn whether the Portfolio is open for business during an emergency situation or unusual event, please call 800-637-1380 or visit northerntrust.com/institutional.

FINANCIAL INTERMEDIARIES. The Trust has authorized Siebert Williams Shank & Co., LLC ("SWS") and certain other financial intermediaries (including banks, trust companies, brokers and investment advisers) to accept purchase, redemption and exchange orders from their customers ("Customers") on behalf of the Portfolio. These authorized intermediaries also may designate other intermediaries to accept such orders, if approved by the Trust. The Portfolio will be deemed to have received an order when the order is accepted by the authorized intermediary, and the order will be priced at the Portfolio’s per share NAV next determined, provided that the authorized intermediary forwards the order (and payment for any purchase order) to the Transfer Agent on behalf of the Trust within agreed-upon time periods. If the order (or payment for any purchase order) is not received by the Transfer Agent within such time periods, the authorized intermediary may be liable for fees and losses and the transaction may be cancelled.

NTI has entered into an agreement with SWS whereby NTI pays SWS a fee for distribution and other services provided by SWS. The additional compensation and payments will be paid to SWS by NTI or its affiliates and will not represent an additional expense to the Portfolio or its shareholders. Such payments may provide an incentive for SWS to recommend shares of the Portfolio when it might not have done so absent such payments.

In addition, Northern Trust may enter into agreements with financial intermediaries through which Customers own shares of the Siebert Williams Shank Shares class of the Portfolio, pursuant to which Northern Trust pays these financial intermediaries for providing certain services. The payments made by Northern Trust to financial intermediaries will be paid by Northern Trust and will not represent an additional expense to the Portfolio or its shareholders.

Northern Trust also may provide compensation to certain dealers for marketing and distribution in connection with the Northern Institutional Funds.

Northern Trust may also sponsor informational meetings, seminars and other similar programs designed to market the Northern Institutional Funds. The amount of such compensation and payments may be made on a one-time and/ or periodic basis, and may represent all or a portion of the annual fees earned by the Investment Adviser (after adjustments). The additional compensation and payments will be paid by Northern Trust or its affiliates and will not represent an additional expense to the Trust or its shareholders. Such payments may provide incentives for financial intermediaries to make shares of the Portfolio available to their Customers, and may allow the Portfolio greater access to such parties and their Customers than would be the case if no payments were paid.

Customers purchasing through a financial intermediary should read their account agreements with the financial intermediary carefully. A financial intermediary's requirements may differ from those listed in this Prospectus. A financial intermediary also may impose account charges, such as asset allocation fees, account maintenance fees, and other charges that will reduce the net return on an investment in the Portfolio. If a Customer has agreed with a particular financial intermediary to maintain a minimum balance and the balance falls below this minimum, the Customer may be required to redeem all or a portion of the Customer's investment in the Portfolio.

Conflict of interest restrictions may apply to the receipt of compensation by a financial intermediary in connection with the investment of fiduciary funds in shares of the Portfolio. Institutions, including banks regulated by the Comptroller of the Currency, Federal Reserve Board and state banking commissions, and investment advisers and other money managers subject to the jurisdiction of the SEC, the Department of Labor or state securities commissions, are urged to consult their legal counsel.

State securities laws regarding the registration of dealers may differ from federal law. As a result, financial intermediaries investing in the Portfolio on behalf of their Customers may be required to register as dealers.

PORTFOLIO HOLDINGS. The Portfolio, or its duly authorized service providers, may publicly disclose holdings of all Northern Institutional Funds in accordance with regulatory requirements,

such as periodic portfolio disclosure in filings with the SEC. The Trust publishes on its website at northerntrust.com/ institutional no later than the fifth business day of each month and for a

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period of not less than six months, a complete schedule of the Portfolio’s holdings and certain other information regarding portfolio holdings of the Portfolio as of the last business day of the prior month. The Portfolio may publish on the Trust’s website a complete schedule of its portfolio holdings and certain other information regarding portfolio holdings more frequently in accordance with the Trust’s policy. Certain portfolio information concerning the Portfolio will be provided in monthly holdings reports to the SEC on Form N-MFP2. Form N-MFP2 will be made available to the public on the SEC’s EDGAR database immediately upon filing after the end of the month to which the information pertains, and a link to each of the most recent 12 months of filings on Form N-MFP2 will be provided on the Trust’s website. A further description of the Trust’s Policy on Disclosure of Portfolio Holdings is available in the SAI.

SHAREHOLDER COMMUNICATIONS. Shareholders of record will be provided each year with a semiannual report showing portfolio investments and other information as of May 31 and with an annual report containing audited financial statements as of November 30. The reports will be made available on the Portfolio’s website at https://www.northerntrust.com/united-states/what-we-do/investment-management/northern-funds/funds-and-performance-institutional/literature . Unless you have elected to receive the reports in paper, you will be notified by mail each time a report is posted and provided a website link to access the report. You may elect to receive future reports in paper free of charge. If you invest through a financial intermediary, you may contact your financial intermediary to continue receiving paper copies of your shareholder reports. If

you invest directly with the Trust, you can inform the Trust that you wish to continue receiving paper copies of your shareholder reports by calling the Northern Institutional Funds Center at 800-637-1380 or by sending an e-mail request to northern-funds@ntrs.com. Your election to receive reports in paper will apply to all Northern Institutional Funds you hold in your account at the financial intermediary or through an account with the Trust.

If we have received appropriate written consent, we send a single copy of all materials, including prospectuses, financial reports, proxy statements or information statements and other notices to all shareholders who share the same mailing address, even if more than one person in a household holds shares of the Portfolio.

If you do not want your mailings combined with those of other members of your household, you may opt-out at any time by contacting the Northern Institutional Funds Center by telephone at 800-637-1380 or by mail at Northern Institutional Funds, P.O. Box 75986, Chicago, Illinois 60675-5986. You also may send an e-mail to northern-funds@ntrs.com. The Portfolio will begin sending individual copies to you within 30 days after receipt of your opt-out notice. The Trust may reproduce this Prospectus in electronic format that may be available on the Internet. If you have received this Prospectus in electronic format you, or your representative, may contact the Transfer Agent for a free paper copy of this Prospectus by writing to the Northern Institutional Funds Center at P.O. Box 75986, Chicago, Illinois 60675-5986, calling 800-637-1380 or by sending an e-mail to: northern-funds@ntrs.com.

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Distributions AND TAX CONSIDERATIONS

DISTRIBUTIONS

Dividends from net income are declared daily and paid monthly by the Portfolio to its shareholders. Net income includes the interest accrued on the Portfolio’s assets less estimated expenses. The Portfolio’s net realized short-term capital gains, if any, are distributed at least annually. The Portfolio does not expect to realize net long-term capital gains.

Dividends are paid as soon as practicable following the end of each month, except in the case of a total redemption of shares in an account that is not subject to a standing order for the purchase of additional shares of the same class. In that event, dividends will be paid promptly along with the redemption proceeds.

All distributions are reinvested automatically (without any sales charge) in additional shares of the same Portfolio, unless you elect to receive distributions in cash by notifying the Transfer Agent in writing. You may make arrangements to credit these distributions to your account with Northern Trust, its affiliates or financial intermediaries.

There are no fees or sales charges on reinvestments.

TAX CONSIDERATIONS

The following is a summary of certain tax considerations that may be relevant to a shareholder in the Portfolio. The discussions of the federal income tax consequences in this Prospectus and the SAI are based on the Internal Revenue Code of 1986, as amended, and the regulations issued under it, and court decisions and administrative interpretations, as in effect on the date of this Prospectus. Future legislative or administrative changes or court decisions may significantly alter the statements included herein, and any such changes or decisions may be retroactive. Except where otherwise indicated, the discussion relates to shareholders who are individual U.S. citizens or residents and is based on current tax law. You should consult your tax professional for further information regarding federal, state, local and/or foreign tax consequences relevant to your specific situation.

DISTRIBUTIONS. The Portfolio intends to qualify as a regulated investment company for federal income tax purposes and to distribute to shareholders substantially all of its net investment income each year. Except as otherwise noted below, you will generally be subject to federal income tax at ordinary rates on a Portfolio’s distributions to you, regardless of whether they are paid in cash or reinvested in Portfolio shares. U.S. individuals with “modified adjusted gross income” exceeding $200,000 ($250,000 if married and filing jointly) and trusts and estates with income above certain thresholds are subject to the Medicare

contribution tax on their “net investment income,” which includes non-exempt interest, dividends and capital gains at a rate of 3.8%. You will be notified annually of the tax status of distributions to you.

The Portfolio generally will be invested in debt instruments and not in shares of stock on which dividend income will be received. As a result, the Portfolio does not expect to pay dividends that are eligible for the reduced tax rate on corporate dividends or that will qualify for the dividends-received deduction for corporations.

IRAS AND OTHER TAX-QUALIFIED PLANS. One major exception to the preceding tax principles is that distributions on shares held in an IRA (or other tax-qualified plan) will not be currently taxable unless shares are acquired with borrowed funds.

REDEMPTIONS. Redemptions are treated as sales for tax purposes and generally are taxable events for shareholders that are subject to tax. In general, if Portfolio shares are sold, a shareholder will recognize gain or loss equal to the difference between the amount realized on the sale and the shareholder’s adjusted tax basis in the shares. As long as the Portfolio maintains a constant NAV of $1.00 per share, generally no gain or loss should be recognized upon the sale of shares of the Portfolio.

BACKUP WITHHOLDING. The Trust will be required in certain cases to withhold and remit to the U.S. Treasury 24% of the dividends and gross sales proceeds paid to any shareholder (i) who had provided either an incorrect tax identification number or no number at all, (ii) who is subject to backup withholding by the Internal Revenue Service for failure to report the receipt of taxable interest or dividend income properly, or (iii) who has failed to certify to the Trust, when required to do so, that he or she is not subject to backup withholding or that he or she is an “exempt recipient.”

U.S. TAX TREATMENT OF FOREIGN SHAREHOLDERS. Portfolio distributions attributable to Portfolio income such as interest will generally be subject to a 30% withholding tax when paid to foreign shareholders. The withholding tax may, however be reduced (and in some cases eliminated) under an applicable tax treaty between the United States and a shareholder’s country of residence or incorporation, provided that the shareholder furnishes the Portfolio with a properly completed Form W-8BEN or W-8BEN-E, as applicable, to establish entitlement for these treaty benefits. Dividends reported as short-term capital gain dividends or interest-related dividends are not subject to U.S. withholding tax. The exemption may not apply, however, if the recipient’s investment in the Portfolio is connected to a trade or business of the recipient in the United States or if the recipient is present in the United States for 183 days or more in a year and certain other conditions are met. However, dividends reported as exempt-interest dividends are generally not subject to U.S. withholding tax. In addition, the Portfolio is required to withhold 30% tax on certain payments to certain foreign entities that do not meet specified information reporting requirements under the Foreign Account Tax Compliance Act.

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SECURITIES, TECHNIQUES AND RISKS

ADDITIONAL INFORMATION ON INVESTMENT OBJECTIVE, PRINCIPAL INVESTMENT STRATEGIES AND RELATED RISKS, DESCRIPTION OF SECURITIES AND COMMON INVESTMENT TECHNIQUES

The following provides additional information regarding the Portfolio’s investment objective, principal investment strategies and related risks discussed in the Portfolio Summary — Principal Investment Strategies section, as well as information about additional investment strategies and techniques that the Portfolio may employ in pursuing its investment objective. Principal investment strategies and risks for the Portfolio are noted in parenthesis. The Portfolio also may make other types of investments to the extent permitted by applicable law. Additional information about the Portfolio, its investment strategies and risks can also be found in the Portfolio’s SAI.

All investments carry some degree of risk that will affect the value of the Portfolio, its yield and investment performance and the price of its shares. An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the FDIC, any other government agency, Siebert Williams Shank & Co., LLC or its affiliates, or Northern Trust, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.

The Portfolio seeks to maintain a stable NAV of $1.00 per share. Consistent with this policy, the Portfolio:

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Limits its dollar-weighted average portfolio maturity to 60 days or less;

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Limits its dollar-weighted average portfolio maturity without regard to maturity shortening provisions applicable to variable and floating rate securities (also known as dollar-weighted average portfolio life) to 120 days or less;

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Buys securities with remaining maturities of 397 days or less or securities otherwise permitted to be purchased because of maturity shortening provisions under Rule 2a-7; and

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Invests only in U.S. dollar-denominated securities that represent minimal credit risks.

SEC regulations require the Portfolio to limit its dollar-weighted average portfolio maturity to 60 days or less, and its dollar-weighted average portfolio life to 120 days or less. The Portfolio also is required to comply with SEC requirements with respect to the liquidity of the Portfolio’s investments. The Portfolio will not acquire any security other than a daily liquid asset unless, immediately following such purchase, at least 10% of its total assets would be invested in daily liquid assets. The Portfolio will not acquire any security other than a weekly liquid asset unless, immediately following such purchase, at least 30% of its total assets would be invested in weekly liquid assets. For these purposes, daily and weekly liquid assets are calculated as of the end of each business day. Daily liquid assets include: cash; direct obligations of the U.S. government; securities that will

mature or are subject to a demand feature that is exercisable and payable within one business day; and amounts receivable and due unconditionally within one business day on pending sales of portfolio securities. Weekly liquid assets include: cash; direct obligations of the U.S. government; certain U.S. government agency discount notes without provision for the payment of interest with remaining maturities of 60 days or less; securities that will mature or are subject to a demand feature that is exercisable and payable within five business days; and amounts receivable and due unconditionally within five business days on pending sales of portfolio securities.

In addition, the Portfolio limits its investments to “Eligible securities” as defined by the SEC. Securities in which the Portfolio may invest may not earn as high a level of income as long-term or lower quality securities, which generally have greater market risk and more fluctuation in market value.

Rule 2a-7 requires money market funds to purchase securities that have a remaining maturity of no more than 397 calendar days (unless otherwise permitted under Rule 2a-7), and (i) which have been determined by a money market fund’s board of trustees (or the fund’s investment adviser, if the board of trustees delegates such power to the adviser) to present minimal credit risks to the fund; (ii) are issued by other investment companies that are money market funds; or (iii) are U.S. government securities. NTI considers several factors including the capacity of each security’s issuer or guarantor to meet its financial obligations.

In accordance with current SEC regulations, the Portfolio generally will not invest more than: (1) 5% of the value of its total assets at the time of purchase in the securities of any single issuer (and certain affiliates of that issuer); and (2) 10% of the value of its total assets at the time of purchase in the securities subject to demand features or guarantees of any single institution. The Portfolio may, however, invest up to 25% of its total assets in the securities of a single issuer for up to three Business Days. These limitations do not apply to cash, certain repurchase agreements, U.S. government securities or securities of other investment companies that are money market funds. In addition, securities subject to demand features and guarantees are subject to different diversification requirements as described in the SAI.

STABLE NAV RISK (principal risk for the Portfolio) is the risk that the Portfolio will not be able to maintain a NAV per share of $1.00 at all times. If the Portfolio fails to maintain a stable NAV (or if there is a perceived threat of such a failure), the Portfolio could be subject to increased redemption activity, which could adversely affect its NAV. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share.

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INVESTMENT OBJECTIVE. The investment objective of the Portfolio may not be changed without shareholder approval.

Under unusual circumstances, the Portfolio may invest less than 50% of its net assets in U.S. government securities that pay interest exempt from state income taxation. The Portfolio may also invest in repurchase agreements that are fully collateralized by cash or U.S. government securities and hold uninvested cash.

During extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be uninvested and will therefore not generate income. The Portfolio may not achieve its investment objective during this time.

ASSET-BACKED SECURITIES. Asset-backed securities are sponsored by entities such as government agencies, banks, financial companies and commercial or industrial companies. Asset-backed securities represent participations in, or are secured by and payable from, pools of assets such as mortgages, motor vehicle installment sale contracts, installment loan contracts, leases of various types of real and personal property, receivables from revolving credit (credit card) agreements, municipal securities and other financial assets.

Such asset pools are securitized through the use of privately-formed trusts or special purpose corporations. Payments or distributions of principal and interest may be guaranteed up to certain amounts and for a certain time period by a letter of credit or a pooled insurance policy issued by a financial institution, or by other credit enhancements.

INVESTMENT STRATEGY. The Portfolio may purchase asset-backed securities (such as mortgage-backed securities) that are issued or guaranteed by the U.S. government or by its agencies, instrumentalities or sponsored enterprises.

SPECIAL RISKS. In addition to credit and market risk, asset-backed securities may involve prepayment risk because the underlying assets (loans) may be prepaid at any time. Prepayment (or call) risk is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) sooner than expected. This may happen during a period of falling interest rates. Accordingly, the Portfolio’s ability to maintain positions in such securities will be affected by reductions in the principal amount of such securities resulting from prepayments, and its ability to reinvest the returns of principal at comparable yields is subject to generally prevailing interest rates at that time.

The value of these securities also may change because of actual or perceived changes in the creditworthiness of the originator, the service agent, the financial institution providing the credit support, or the counterparty. Unlike mortgage-backed securities issued or guaranteed by agencies of the U.S. government or government-sponsored enterprises, mortgage-backed securities issued by private issuers do not have a government or government-sponsored enterprise guarantee (but may have other credit enhancement), and may, and frequently do, have less favorable collateral, credit risk or other underwriting

characteristics. Credit supports generally apply only to a fraction of a security’s value. Like other fixed-income securities, when interest rates rise, the value of an asset-backed security generally will decline. However, when interest rates decline, the value of an asset-backed security with prepayment features may not increase as much as that of other fixed-income securities. In addition, non-mortgage asset-backed securities involve certain risks not presented by mortgage-backed securities. Primarily, these securities do not have the benefit of the same security interest in the underlying collateral. Credit card receivables generally are unsecured, and the debtors are entitled to the protection of a number of state and federal consumer credit laws.

Automobile receivables are subject to the risk that the trustee for the holders of the automobile receivables may not have an effective security interest in all of the obligations backing the receivables. If the issuer of the security has no security interest in the related collateral, there is the risk that the Portfolio could lose money if the issuer defaults. The economic recession that commenced in the United States in 2008, introduced a period of heightened levels of default on the receivables and loans underlying asset-backed securities than were historically experienced. A future economic downturn could increase the risk that such assets underlying asset-backed securities purchased by the Portfolio would also suffer greater levels of default than were historically experienced. In addition to prepayment risk, investments in mortgage-backed securities comprised of subprime mortgages and investments in other asset-backed securities of underperforming assets may be subject to a higher degree of credit risk, valuation risk and liquidity risk.

BORROWINGS AND REVERSE REPURCHASE AGREEMENTS. The Portfolio may borrow money from banks and may enter into reverse repurchase agreements with banks and other financial institutions.

INVESTMENT STRATEGY. The Portfolio may borrow money from banks and enter into reverse repurchase agreements with banks and other financial institutions in amounts not exceeding one-fourth of the value of its total assets (including the amount borrowed). The Portfolio may enter into reverse repurchase agreements when the Investment Adviser expects that the interest income to be earned from the investment of the transaction proceeds will be greater than the related interest expense.

SPECIAL RISKS. Borrowings and reverse repurchase agreements involve leveraging. Reverse repurchase agreements involve the sale of money market securities held by the Portfolio subject to the Portfolio’s agreement to repurchase them at a mutually agreed upon date and price (including interest). If the securities held by the Portfolio decline in value while these transactions are outstanding, the NAV of the Portfolio’s outstanding shares will decline in value by proportionately more than the decline in value of the securities. In addition, reverse repurchase agreements involve the risks that (a) the interest income earned by the Portfolio (from the investment of the proceeds) will be less than the interest expense of the transaction; (b) the market

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value of the securities sold by the Portfolio will decline below the price the Portfolio is obligated to pay to repurchase the securities; and (c) the securities may not be returned to the Portfolio.

CREDIT FACILITY AND BORROWING. The portfolios of the Trust, including the Portfolio, and affiliated funds of Northern Funds (each a “Fund”, and together the “Funds”) have jointly entered into a revolving credit facility (the “Credit Facility”) whereby the Portfolio, the other portfolios in the Trust, and the Funds may borrow for the temporary funding of shareholder redemptions or for other temporary or emergency purposes. Pursuant to the Credit Facility, the participating portfolios and Funds may borrow up to an aggregate commitment amount of $250 million (the “Commitment Limit”) at any time, subject to asset coverage and other limitations as specified in the Credit Facility and under the 1940 Act. The Portfolio may borrow up to the maximum amount allowable under their current prospectuses and SAIs, subject to various other legal, regulatory or contractual limits, including the asset coverage limits in the Credit Facility.

Borrowing results in interest expense and other fees and expenses for the Portfolio that may impact the Portfolio’s expenses, including any net expense ratios. The costs of borrowing may reduce the Portfolio’s yield. If the Portfolio borrows pursuant to the Credit Facility, it is charged interest at a variable rate. The Portfolio also pays a commitment fee equal to its pro rata share of the unused portion of the Credit Facility. The availability of funds under the Credit Facility can be affected by other participating portfolios’ or Funds’ borrowings under the Credit Facility. As such, the Portfolio may be unable to borrow (or borrow further) under the Credit Facility if the Commitment Limit has been reached.

CREDIT (OR DEFAULT) RISK (principal risk for the Portfolio) is the risk that an issuer of fixed-income securities held by the Portfolio may default on its obligation to pay interest and repay principal. Generally, the lower the credit rating of a security, the greater the risk that the issuer of the security will default on its obligation. High quality securities are generally believed to have relatively low degrees of credit risk. The Portfolio intends to enter into financial transactions with counterparties that are creditworthy at the time of the transactions. There is always the risk that the Investment Adviser’s analysis of creditworthiness is incorrect or may change due to market conditions. Concerns over an issuer’s ability to make principal or interest payments may cause the value of a fixed income security to decline. To the extent that the Portfolio focuses its transactions with a limited number of counterparties, it will be more susceptible to the risks associated with one or more counterparties. In addition, the Portfolio may incur expenses in an effort to protect the Portfolio’s interests or enforce its rights against an issuer, guarantor or counterparty or may be hindered or delayed in exercising these rights.

CUSTODIAL RECEIPTS FOR TREASURY SECURITIES. Custodial receipts are participations in trusts that hold U.S. Treasury securities and are sold under such names as TIGRs (Treasury

Income Growth Receipts) and CATS (Certificates of Accrual on Treasury Securities). Like other stripped obligations, they entitle the holder to future interest payments or principal payments on the U.S. Treasury securities.

INVESTMENT STRATEGY. To the extent consistent with its investment objectives and strategies, the Portfolio may invest a portion of its assets in custodial receipts.

SPECIAL RISKS. Like other stripped securities (which are described below), stripped custodial receipts may be subject to greater price volatility than ordinary debt obligations because of the way in which their principal and interest are returned to investors. Custodial receipts may not be considered obligations of the U.S. government or other issuer of the security held by the custodian for the purposes of securities laws. If for tax purposes, the Portfolio is not considered to be the owner of the securities held in the underlying trust or custodial account, the Portfolio may suffer adverse tax consequences. As a holder of custodial receipts, the Portfolio will bear its proportionate share of the fees or expenses charged to the custodial account.

CYBERSECURITY RISK (principal risk for the Portfolio). With the increased use of the Internet and because information technology (“IT”) systems and digital data underlie most of the Portfolio’s operations, the Portfolio and its investment adviser, custodian, transfer agent, distributor and other service providers and the financial intermediaries of each (collectively “Service Providers”) are exposed to the risk that their operations and data may be compromised as a result of internal and external cyber-failures, breaches or attacks (“Cyber Risk”). This could occur as a result of malicious or criminal cyberattacks. Cyber-attacks include actions taken to: (i) steal or corrupt data maintained online or digitally, (ii) gain unauthorized access to or release confidential information, (iii) shut down the Portfolio or Service Provider website through denial-of-service attacks, or (iv) otherwise disrupt normal business operations. However, events arising from human error, faulty or inadequately implemented policies and procedures or other systems failures unrelated to any external cyber-threat may have effects similar to those caused by deliberate cyber-attacks.

Successful cyber-attacks or other cyber-failures or events affecting the Portfolio or its Service Providers may adversely impact the Portfolio or its shareholders. For instance, such attacks, failures or other events may interfere with the processing of shareholder transactions, impact the Portfolio’s ability to calculate its NAV, cause the release of private shareholder information or confidential Portfolio information, impede trading, or cause reputational damage. Such attacks, failures or other events could also subject the Portfolio or its Service Providers to regulatory fines, penalties or financial losses, reimbursement or other compensation costs, and/or additional compliance costs. Insurance protection and contractual indemnification provisions may be insufficient to cover these losses. The Portfolio or its Service Providers may also incur significant costs to manage and control Cyber Risk. While the Portfolio and its Service Providers have established IT and data

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security programs and have in place business continuity plans and other systems designed to prevent losses and mitigate Cyber Risk, there are inherent limitations in such plans and systems, including the possibility that certain risks have not been identified or that cyber-attacks may be highly sophisticated. Furthermore, the Portfolio has limited ability to prevent or mitigate cybersecurity incidents affecting Service Providers, and such Service Providers may have limited indemnification obligations to the Portfolio or its investment adviser, and the Portfolio cannot control the cybersecurity plans and systems put in place by the Service Providers or any other third parties whose operations may affect the Portfolio or its shareholders. The Portfolio and its shareholders could be negatively impacted as a result.

Cyber Risks are also present for issuers of securities or other instruments in which the Portfolio invests, which could result in material adverse consequences for such issuers, and may cause the Portfolio’s investment in such issuers to lose value.

DERIVATIVES. The Portfolio may purchase certain “derivative” instruments. A derivative is a financial instrument whose value is derived from, or based upon, the performance of underlying assets, interest rates, or other indices. Derivatives include structured securities such as collateralized mortgage obligations and other types of asset-backed securities, “stripped” securities and various floating rate instruments.

INVESTMENT STRATEGY. The Portfolio may invest in derivatives when the Investment Adviser believes the potential risks and rewards are consistent with the Portfolio’s objective, strategies and overall risk profile.

SPECIAL RISKS. Engaging in derivative transactions involves special risks, including (a) market risk that the Portfolio’s derivatives position will lose value; (b) credit risk that the counterparty to the transaction will default; (c) leveraging risk that the value of the derivative instrument will decline more than the value of the assets on which it is based; (d) risks pertaining to illiquid investments that the Portfolio will be unable to sell its position because of lack of market depth or disruption; (e) pricing risk that the value of a derivative instrument will be difficult to determine; and (f) operations risk that loss will occur as a result of inadequate systems or human error. Many types of derivatives have been developed recently and have not been tested over complete market cycles. For these reasons, the Portfolio may suffer a loss whether or not the analysis of the Investment Adviser is accurate.

GUARANTOR (OR CREDIT ENHANCEMENT) RISK. Guarantor (or credit enhancement risk) is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments in securities backed by guarantees, letters of credit, insurance or other credit enhancements issued by such bank or institution to decline in value. Guarantees, letters of credit, insurance or other credit enhancements do not protect the Portfolio or its shareholders

from losses caused by declines in a security’s market value. In addition, having multiple securities’ credit enhanced by the same enhancement provider will increase the adverse effects on the Portfolio that are likely to result from a downgrading of, or a default by, such enhancement provider. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio.

ILLIQUID OR RESTRICTED INVESTMENTS. An illiquid investment is an investment that the Portfolio reasonably expects cannot be sold or disposed of in the ordinary course of business within seven calendar days at approximately the value ascribed to it by the Portfolio. Illiquid investments include repurchase agreements and time deposits with notice/termination dates of more than seven days, certain variable amount master demand notes that cannot be called within seven days, certain insurance funding agreements, derivative instruments, and securities and other financial instruments that are not readily marketable, and 144A Securities (as defined below), and both foreign and domestic securities that are not readily marketable, unless, based upon a review of the relevant market, trading and investment-specific considerations, those investments are determined not to be illiquid.

INVESTMENT STRATEGY. The Portfolio may invest up to 5% of its total assets in illiquid investments, as such term is defined in Rule 2a-7 under the 1940 Act. A domestically traded security that is not registered under the Securities Act of 1933, as amended (the “1933 Act”) will not be considered illiquid if the Investment Adviser determines that an adequate trading market exists for that security. If otherwise consistent with its investment objective and strategies, the Portfolio may purchase commercial paper issued pursuant to Section 4(a)(2) of the 1933 Act and securities that are not registered under the 1933 Act but can be sold to “qualified institutional buyers” in accordance with Rule 144A under the 1933 Act (“Rule 144A Securities”). These securities will not be considered illiquid so long as the Investment Adviser determines, that under guidelines approved by the Trust’s Board of Trustees, an adequate trading market exists.

SPECIAL RISKS. Because illiquid and restricted investments may be difficult to sell at an acceptable price, they may be subject to greater volatility and may result in a loss to the Portfolio. The practice of investing in Rule 144A Securities and commercial paper available to qualified institutional buyers could increase the level of the Portfolio’s illiquidity during any period that qualified institutional buyers become uninterested in purchasing these securities. Investments purchased by the Portfolio that are liquid at the time of purchase may subsequently become illiquid due to events relating to the issuer, market events, economic conditions and/or investor perception. To the extent an investment held by the Portfolio is deemed to be an illiquid investment or a less liquid investment, the Portfolio will be exposed to greater liquidity risk.

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INCOME RISK (principal risk for the Portfolio) is the risk that the Portfolio’s ability to distribute income to shareholders depends on the yield available from the Portfolio’s investments. Falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities.

INTEREST RATE RISK (principal risk for the Portfolio). The Portfolio’s yield will vary with changes in interest rates. During periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher. In a period of rising interest rates, the Portfolio’s yield may not rise as quickly as the yields of certain other short-term investments. Investments held by the Portfolio with longer maturities will tend to be more sensitive to interest rate changes than investments with shorter maturities. If interest rates rise, the Portfolio’s yield may not increase proportionately.

Interest rates in the U.S. are currently at historically low levels. A low or negative interest rate environment poses additional risks to the Portfolio, which are heightened in a very low or negative interest rate environment. Changing interest rates may have unpredictable effects on the markets and the Portfolio’s investments. A low interest rate environment may cause the Portfolio’s earnings to fall below the Portfolio’s expense ratio, resulting in a low or negative yield and a decline in the Portfolio’s share price. Additionally, securities issued or guaranteed by the U.S. government, its agencies, instrumentalities and sponsored enterprises have historically involved little risk of loss of principal if held to maturity. However, due to fluctuations in interest rates, the market value of such securities held by the Portfolio may vary.

INTERFUND BORROWING AND LENDING. The SEC has granted an exemption permitting the Portfolio to participate in an interfund borrowing and lending program. This interfund borrowing and lending program allows the Portfolio to borrow money from other portfolios in the Trust and other affiliated funds of Northern Funds (each a “Fund” and together the “Funds”) advised by NTI, and to lend money to other portfolios in the Trust, for temporary or emergency purposes. The interfund borrowing and lending program is currently not operational. The interfund borrowing and lending program is subject to a number of conditions, including, among other things, the requirements that (1) the Portfolio may not borrow or lend money through the program unless it receives a more favorable interest rate than is available from a bank loan rate or investment yield rate, respectively; (2) loans will be secured on an equal priority basis with at least an equivalent percentage of collateral to loan value as any outstanding bank loan that requires collateral; (3) loans will have a maturity no longer than that of any outstanding bank loan (and in any event not over seven days); (4) if an event of default occurs under any agreement evidencing an outstanding bank loan to the Portfolio, the event of default will automatically (without need for action or notice by the lending Portfolio or Fund) constitute an immediate event of default under the Interfund Lending

Agreement entitling the lending Portfolio or Fund to call the interfund loan (and exercise all rights with respect to any collateral) and that such call will be made if the bank exercises its right to call its loan under its agreement with the Portfolio; (5) the Portfolio may not borrow money if the loan would cause its outstanding borrowings from all sources to exceed 10% of its net assets at the time of the loan, except that the Portfolio may borrow up to 33 1/3% of its total assets through the program or from other sources if each interfund loan is secured by the pledge of segregated collateral with a market value of at least 102% of the outstanding principal value of the loan; (6) the Portfolio may not loan money if the loan would cause its aggregate outstanding loans through the program to exceed 15% of its net assets at the time of the loan; (7) the Portfolio’s interfund loans to any one portfolio shall not exceed 5% of the lending Portfolio’s net assets; and (8) the Portfolio’s borrowings through the program will not exceed the greater of 125% of the Portfolio’s total net cash redemptions or 102% of the Portfolio’s sales fails (when a sale of securities “fails,” due to circumstances beyond the Portfolio’s control) for the preceding seven calendar days as measured at the time of the loan. In addition, the Portfolio may participate in the interfund borrowing and lending program only if and to the extent that such participation is consistent with the Portfolio’s investment objective and policies. The Board of Trustees of the Trust is responsible for overseeing the interfund borrowing and lending program. A delay in repayment to a lending Portfolio could result in a lost investment opportunity or additional lending costs.

INVESTMENT COMPANIES. To the extent consistent with its investment objective and strategies, the Portfolio may invest in securities issued by other affiliated or unaffiliated investment companies.

INVESTMENT STRATEGY. Investments by the Portfolio in other investment companies will be subject to the limitations of the 1940 Act and SEC orders. Although the Portfolio does not expect to do so in the foreseeable future, the Portfolio is authorized to invest substantially all of its assets in an open-end investment company or a series thereof that has substantially the same investment objective, strategies and fundamental restrictions as the Portfolio.

SPECIAL RISKS. As a shareholder of another investment company, the Portfolio would be subject to the same risks as any other investor in that company. It would also bear a proportionate share of any fees or expenses paid by that company. These expenses would be in addition to the management fees and other expenses the Portfolio bears directly in connection with its own

operations. In October 2020, the SEC adopted certain regulatory changes and took other actions related to the ability of an investment company to invest in another investment company. These regulatory changes may adversely impact the Portfolio’s investment strategies and operations.

LARGE SHAREHOLDER RISK (principal risk for the Portfolio). To the extent a significant percentage of the shares of the Portfolio are owned or controlled by a small number of account

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shareholders (or a single account shareholder), including funds or accounts over which the Investment Adviser or an affiliate of the Investment Adviser has investment discretion, the Portfolio is subject to the risk that those shareholders may purchase or redeem Portfolio shares in significant amounts rapidly or unexpectedly, including as a result of an asset allocation decision made by the Investment Adviser or an affiliate of the Investment Adviser and may adversely affect the Portfolio’s performance if the Investment Adviser is forced to sell portfolio securities or invest cash when the Investment Adviser would not otherwise choose to do so. Redemptions of a large number of shares may affect the liquidity of the Portfolio, increase the Portfolio’s transaction costs, and accelerate the realization of taxable income and/or gains. Such sales may also accelerate the realization of taxable income to shareholders if these sales result in gains, and may also increase transaction costs. In addition, a large redemption could result in the Portfolio’s current expenses being allocated over a smaller asset base, leading to an increase in the Portfolio’s expense ratio. Similarly, large purchases of the Portfolio’s shares may adversely affect the Portfolio’s performance to the extent that the Portfolio is delayed in investing new cash or otherwise maintains a larger cash position than it ordinarily would.

LIBOR TRANSITION. The Portfolio’s investments, payment obligations and financing terms may be based on floating rates, such as London Interbank Offered Rate (“LIBOR”), Euro Interbank Offered Rate and other similar types of reference rates (each, a “Reference Rate”). On July 27, 2017, the Chief Executive of the United Kingdom (“UK”) Financial Conduct Authority (“FCA”), which regulates LIBOR, announced that the FCA will no longer persuade nor compel banks to submit rates for the calculation of LIBOR and certain other Reference Rates after the end of 2021. Such announcement indicates that the continuation of LIBOR and other Reference Rates on the current basis cannot and will not be guaranteed starting in 2022. The transition away from LIBOR and other Reference Rates may lead to increased volatility and illiquidity in markets that are tied to such Reference Rates and reduced values of Reference Rate-related investments. This announcement and any additional regulatory or market changes that occur as a result of the transition away from Reference Rates may have an adverse impact on the Portfolio’s investments, performance or financial condition.

LIQUIDITY RISK. Liquidity risk is the risk that the Portfolio will not be able to pay redemption proceeds within the time periods described in this Prospectus because of unusual market conditions, an unusually high volume of redemption requests, legal restrictions impairing its ability to sell particular securities or close derivative positions at an advantageous market price or other reasons. Certain portfolio securities may be less liquid than others, which may make them difficult or impossible to sell at the time and the price that the Portfolio would like or difficult to value. The Portfolio may have to lower the price, sell other securities instead or forgo an investment opportunity. In addition, certain assets that the Portfolio wants to buy may be difficult or impossible to purchase. Any of these events could

have a negative effect on portfolio management or performance. Liquidity risk may be the result of, among other things, the reduced number and capacity of traditional market participants to make a market in fixed income securities. As a general matter, dealers recently have been less willing to make markets for fixed income securities. The potential for liquidity risk may be magnified by a rising interest rate environment or other circumstances where investor redemptions from money market and other fixed income mutual funds may be higher than normal, potentially causing increased supply in the market due to selling activity. Portfolios with principal investment strategies that involve investments in securities of companies with smaller market capitalizations, foreign securities, derivatives or securities with potential market and/or credit risk tend to have the greatest exposure to liquidity risk. All of these risks may increase during periods of market volatility. The liquidity of certain assets, such as privately issued and non-investment grade mortgage-and asset-backed securities, may be difficult to ascertain and may change over time. Transactions in less liquid securities may entail transaction costs that are higher than those for transactions in more liquid securities.

MARKET EVENTS RISK. Market events risk relates to the increased volatility, depressed valuations, decreased liquidity and heightened uncertainty in the financial markets throughout the world during the past decade. These conditions may recur.

The U.S. government and the Federal Reserve, as well as certain foreign governments and central banks, have taken steps to support financial markets, including by keeping interest rates at historically low levels. This and other government intervention may not work as intended, particularly if the efforts are perceived by investors as being unlikely to achieve the desired results. Certain foreign governments and central banks have implemented so-called negative interest rates (e.g., charging depositors who keep their cash at a bank) to spur economic growth. Governmental or central bank actions, including interest rate increases, measures to address budget deficits, or contrary actions by different governments, as well as downgrades of sovereign debt, fluctuations in oil and commodity prices, dramatic changes in currency exchange rates and geopolitical events (including war and terror attacks) could negatively affect financial markets generally, increase market volatility and reduce the value and liquidity of securities in which the Portfolio invests.

Policy and legislative changes in the United States and in other countries (such as Brexit, as further discussed below) may also contribute to decreased liquidity and increased volatility in the financial markets. Political turmoil within the U.S. and abroad may also impact the Portfolio. Although the U.S. government has historically honored its credit obligations, it remains possible that the U.S. could default on its obligations. While it is impossible to predict the consequences of such an unprecedented event, it is likely that a default by the U.S. would be highly disruptive to the U.S. and global securities markets and could significantly impair the value of the Portfolio’s investments. Similarly, political events within the United States at times have resulted, and may in the future result, in a shutdown of

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government services, which could negatively affect the U.S. economy, decrease the value of many Portfolio investments, and increase uncertainty in or impair the operation of the U.S. or other securities markets.

Economies and financial markets throughout the world are increasingly interconnected. Economic, financial or political events, trading and tariff arrangements, terrorism, natural disasters, public health emergencies (including pandemics and epidemics) and other circumstances in one country or region could have profound impacts on global economies or markets. As a result, whether or not the Portfolio directly invests in securities of issuers located in or with significant exposure to the countries directly affected, the value and liquidity of the Portfolio’s investments may be negatively affected.

In June 2016, the UK approved a referendum to leave the EU. The withdrawal, known colloquially as "Brexit", was agreed to and ratified by the UK Parliament, and the UK left the EU on January 31, 2020. It began a transition period in which to negotiate a new trading relationship for goods and services that ended on December 31, 2020. On January 1, 2021, the UK left the EU Single Market and Customs Union, as well as all EU policies and international agreements. On December 24, 2020, the UK and EU agreed to a trade deal with no tariffs or quotas on products, regulatory and customs cooperation mechanisms as well as provisions ensuring a level playing field for open and fair competition. The UK and EU also plan to put in place a regulatory dialogue on financial systems based on a separate memorandum of understanding in 2021. Since the referendum, there have been periods of significant volatility in the global stock markets and currency exchange rates, as well as challenging market conditions in the UK. At this time, the impact that the trade deal and any future agreements on services, particularly financial services, will have on the Portfolio cannot be predicted, and it is possible that the new terms may adversely affect the Portfolio.

RECENT MARKET EVENTS. Periods of unusually high financial market volatility and restrictive credit conditions, at times limited to a particular sector or geographic area, have occurred in the past and may be expected to recur in the future. Some countries, including the United States, have adopted or have signaled protectionist trade measures, relaxation of the financial industry regulations that followed the financial crisis, and/or reductions to corporate taxes. The scope of these policy changes is still developing, but the equity and debt markets may react strongly to expectations of change, which could increase volatility, particularly if a resulting policy runs counter to the market’s expectations. The outcome of such changes cannot be foreseen at the present time. In addition, geopolitical and other risks, including environmental and public health risks, may add to instability in the world economy and markets generally. As a result of increasingly interconnected global economies and financial markets, the value and liquidity of the Portfolio’s

investments may be negatively affected by events impacting a country or region, regardless of whether the Portfolio invests in issuers located in or with significant exposure to such country or region.

Recent events are impacting the securities markets. An outbreak of respiratory disease caused by a novel coronavirus was first detected in December 2019 and has spread internationally. The outbreak and efforts to contain its spread have resulted in closing borders and quarantines, restricting international and domestic travel, enhanced health screenings, cancellations, disrupted supply chains and customer activity, responses by businesses (including changes to operations and reducing staff), and have produced general concern and uncertainty. The impact of the coronavirus pandemic, and other epidemics and pandemics that may arise in the future, could adversely affect national and global economies, individual companies and the market in general in a manner and for a period of time that cannot be foreseen at the present time. Health crises caused by the outbreak may heighten other pre-existing political, social and economic risks in a country or region. Governmental authorities and regulators throughout the world, such as the U.S. Federal Reserve, have in the past responded to major economic disruptions with changes to fiscal and monetary policy, including but not limited to, direct capital infusions, new monetary programs, and dramatically lower interest rates. Certain of those policy changes are being implemented in response to the coronavirus outbreak. Such policy changes may adversely affect the value, volatility and liquidity of dividend and interest paying securities. In certain cases, an exchange or market may close or issue trading halts on either specific securities or even the entire market, which may result in the Portfolio being, among other things, unable to buy or sell certain securities or financial instruments or to accurately price its investments. In the event of a pandemic or an outbreak, there can be no assurance that the Portfolio and its service providers will be able to maintain normal business operations for an extended period of time or will not lose the services of key personnel on a temporary or long-term basis due to illness or other reasons. A pandemic or disease could also impair the information technology and other operational systems upon which the Portfolio’s investment adviser relies, and could otherwise disrupt the ability of the Portfolio’s service providers to perform essential tasks. Although multiple asset classes may be affected by a market disruption, the duration and effects may not be the same for all types of assets. To the extent the Portfolio may overweight its investments in certain countries, companies, industries or market sectors, such position will increase the Portfolio’s exposure to risk of loss from adverse developments affecting those countries, companies, industries or sectors. These conditions could result in the Portfolio’s inability to achieve its investment objectives, cause the postponement of reconstitution or rebalance dates for benchmark indices, adversely affect the prices and liquidity of the securities and other instruments in which the Portfolio invests, negatively impacting the Portfolio’s performance, and cause losses on your investments in the Portfolio. You should also review this prospectus and the SAI to

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understand the Portfolio’s discretion to implement temporary defensive measures, as well as the circumstances in which the Portfolio may satisfy redemption requests in-kind.

OPERATIONAL RISK. The Investment Adviser to the Portfolio and other Portfolio service providers may be subject to operational risk and may experience disruptions and operating errors. In particular, these errors or failures in systems and technology, including operational risks associated with reliance on third party service providers, may adversely affect the Portfolio’s ability to calculate its NAV in a timely manner, including over a potentially extended period. Moreover, disruptions (for example, pandemics and health crises) that cause prolonged periods of remote work or significant employee absences at the Portfolio’s service providers could impact the ability to conduct the Portfolio’s operations. While service providers are required to have appropriate operational risk management policies and procedures in place, their methods of operational risk management may differ from those of the Portfolio in the setting of priorities, the personnel and resources available or the effectiveness of relevant controls. The Investment Adviser, through its monitoring and oversight of service providers, seeks to ensure that service providers take appropriate precautions to avoid and mitigate risks that could lead to disruptions and operating errors. However, it is not possible for the Investment Adviser or other Portfolio service providers to identify all of the operational risks that may affect the Portfolio or to develop processes and controls to completely eliminate or mitigate their occurrence or effects.

PREPAYMENT (OR CALL) RISK (principal risk for the Portfolio) is the risk that prepayment of the underlying mortgages or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities. As interest rates fall and certain obligations are paid off by obligors more quickly than originally anticipated, the Portfolio may invest the proceeds in securities with lower yields.

REPURCHASE AGREEMENTS (principal strategy for the Portfolio). Repurchase agreements involve the purchase of securities by the Portfolio subject to the seller’s agreement to repurchase them at a mutually agreed upon date and price.

INVESTMENT STRATEGY. To the extent consistent with its investment objective and principal investment strategies, the Portfolio may enter into repurchase agreements with domestic and foreign financial institutions such as banks and broker-dealers that are deemed to be creditworthy by the Investment Adviser. Although the securities subject to a repurchase agreement may have maturities exceeding one year, settlement of the agreement generally will not occur more than one year after the Portfolio acquires the securities.

SPECIAL RISKS. In the event of a default, the Portfolio will suffer a loss to the extent that the proceeds from the sale of the underlying securities and other collateral are less than the repurchase price and the Portfolio’s costs associated with delay and enforcement of the repurchase agreement. In addition, in the

event of bankruptcy, the Portfolio could suffer additional losses if a court determines that the Portfolio’s interest in the collateral is unenforceable by the Portfolio. If the Portfolio enters into a repurchase agreement with a foreign financial institution, it may be subject to the same risks associated with foreign investments.

Certain foreign markets may rely heavily on particular industries or foreign capital and are more vulnerable to diplomatic developments, the imposition of economic sanctions against a particular country or countries, organizations, entities and/or individuals, changes in international trading patterns, trade barriers, and other protectionist or retaliatory measures. International trade barriers or economic sanctions against foreign countries, organizations, entities and/or individuals may adversely affect the credit worthiness of a foreign financial institution. Additionally, foreign banks and foreign branches of domestic banks may be subject to less stringent reserve requirements and to different accounting, auditing and recordkeeping requirements.

The Portfolio intends to enter into transactions with counterparties that are creditworthy at the time of the transactions. There is always the risk that the Investment Adviser’s analysis of creditworthiness is incorrect or may change due to market conditions. To the extent that the Portfolio focuses its transactions with a limited number of counterparties, it will be more susceptible to the risks associated with one or more counterparties.

With respect to collateral received in repurchase transactions or other investments, the Portfolio may have significant exposure to the financial services and mortgage markets. Such exposure, depending on market conditions, could have a negative impact on the Portfolio, including minimizing the value of any collateral.

STRIPPED SECURITIES. These securities are issued by the U.S. government (or an agency, instrumentality or a sponsored enterprise), foreign governments, banks and other issuers.

They entitle the holder to receive either interest payments or principal payments that have been “stripped” from a debt obligation. These obligations include stripped mortgage-backed securities, which are derivative multi-class mortgage securities.

The Treasury Department has facilitated transfers of ownership of zero coupon securities by accounting separately for the beneficial ownership of particular interest coupon and principal payments on Treasury securities through the Federal Reserve book-entry record-keeping system. The Federal Reserve program as established by the Treasury Department is known as “Separate Trading of Registered Interest and Principal of Securities” or “STRIPS.” Under the STRIPS program, the Portfolio will be able to have its beneficial ownership of zero coupon securities recorded directly in the book-entry record-keeping system in lieu of having to hold certificates or other evidences of ownership of the underlying U.S. Treasury securities.

U.S. Government Select Portfolio 26 Northern Institutional Funds Prospectus

U.S. Government Select Portfolio–Siebert Williams shank Shares

INVESTMENT STRATEGY. To the extent consistent with its investment objective and strategies, the Portfolio may purchase stripped securities, including securities registered in the STRIPS program.

SPECIAL RISKS. Stripped securities are very sensitive to changes in interest rates and to the rate of principal prepayments. A rapid or unexpected change in either interest rates or principal prepayments could depress the price of stripped securities held by the Portfolio and adversely affect the Portfolio’s investment performance.

STRUCTURED SECURITIES. The value of such securities is determined by reference to changes in the value of specific currencies, interest rates, commodities, securities, indices or other financial indicators (the “Reference”) or the relative change in two or more References. The interest rate or the principal amount payable upon maturity or redemption may be increased or decreased depending upon changes in the applicable Reference. Examples of structured securities include, but are not limited to, asset-backed commercial paper, structured notes and other debt obligations where the principal repayment at maturity is determined by the value of a specified security or securities index.

INVESTMENT STRATEGY. The Portfolio may invest in structured securities to the extent consistent with its investment objective and strategies.

SPECIAL RISKS. Structured securities present additional risk that the interest paid to the Portfolio on a structured security will be less than expected. The terms of some structured securities may provide that in certain circumstances no principal is due at maturity and, therefore, the Portfolio could suffer a total loss of its investment. Structured securities may be positively or negatively indexed, so that appreciation of the Reference may produce an increase or decrease in the interest rate or value of the security at maturity. In addition, changes in the interest rates or the value of the security at maturity may be a multiple of changes in the value of the Reference. Consequently, structured securities may entail a greater degree of market risk than other types of securities. Structured securities also may be more volatile, less liquid and more difficult to accurately price than less complex securities due to their derivative nature.

TEMPORARY INVESTMENTS. For capital preservation and liquidity, the Portfolio may have a greater concentration in short-term securities, including investing up to all of its assets in overnight securities, which may result in a reduction of the Portfolio’s yield.

Although the Investment Adviser has the ability to take temporary positions, it may choose not to do so for a variety of reasons, even during volatile market conditions.

U.S. GOVERNMENT OBLIGATIONS (principal risk for the Portfolio). These instruments include U.S. Treasury obligations, such as bills, notes and bonds, which generally differ only in terms of their interest rates, maturities and time of issuance.

They also include obligations issued or guaranteed by the U.S. government or by its agencies, instrumentalities or sponsored enterprises. Securities guaranteed as to principal and interest by the U.S. government or by its agencies, instrumentalities or sponsored enterprises are deemed to include (a) securities for which the payment of principal and interest is backed by an irrevocable letter of credit issued by the U.S. government or by an agency, instrumentality or sponsored enterprise thereof and (b) participations in loans made to foreign governments or their agencies that are so guaranteed. U.S. treasury obligations also include floating rate public obligations of the U.S. Treasury.

INVESTMENT STRATEGY. To the extent consistent with its investment objective and strategies, the Portfolio may invest in a variety of U.S. Treasury obligations and in other obligations issued or guaranteed by the U.S. government or by its agencies, instrumentalities or sponsored enterprises.

SPECIAL RISKS. Not all U.S. government obligations carry the same credit support. Although many U.S. government securities are issued by entities chartered or sponsored by Acts of Congress, such as the Federal National Mortgage Association (“Fannie Mae”), the Federal Home Loan Mortgage Corporation (“Freddie Mac”) and the Federal Home Loan Banks, such securities are neither issued nor guaranteed by the U.S. Treasury and, therefore, are not backed by the full faith and credit of the United States. Some, such as those of the Government National Mortgage Association (“Ginnie Mae”), are supported by the full faith and credit of the U.S. Treasury, although this guarantee applies only to principal and interest payments and does not apply to losses resulting from declines in the market value of these securities. Other obligations, such as those of the Federal Home Loan Banks, are supported by the right of the issuer to borrow from the U.S. Treasury; and others are supported by the discretionary authority of the U.S. government to purchase the agency’s obligations. Still others are supported only by the credit of the instrumentality or sponsored enterprise. The maximum potential liability of the issuers of some U.S. government securities may greatly exceed their current resources, including their legal right to support from the U.S. Treasury. It is possible that these issuers will not have the funds to meet their payment obligations in the future. No assurance can be given that the U.S. government would provide financial support to its agencies, instrumentalities or sponsored enterprises if it is not obligated to do so by law. In addition, the secondary market for certain participations in loans made to foreign governments or their agencies may be limited.

An agency of the U.S. government has placed Fannie Mae and Freddie Mac into conservatorship, a statutory process with the objective of returning the entities to normal business operations. It is unclear what effect this conservatorship will have on the securities issued or guaranteed by Fannie Mae or Freddie Mac. As a result, these securities are subject to more credit risk than U.S. government securities that are supported by the full faith and credit of the United States (e.g., U.S. Treasury bonds). To the extent the Portfolio invests in debt instruments or securities of non-U.S. government entities that are backed by the full faith

Northern Institutional Funds Prospectus 27 U.S. Government Select Portfolio

U.S. Government Select Portfolio–Siebert Williams shank Shares

and credit of the United States, pursuant to the FDIC Debt Guarantee Program (the “Debt Guarantee Program”) or other similar programs, there is a possibility that the guarantee provided under the Debt Guarantee Program or other similar programs may be discontinued or modified at a later date.

Floating rate public obligations of the U.S. Treasury (“Floating Rate Notes” or “FRNs”) have interest rates that adjust periodically. FRNs’ floating interest rates may be higher or lower than the interest rates of fixed-rate bonds of comparable quality with similar maturities. Securities with floating rates can be less sensitive to interest rate changes than securities with fixed interest rates, but may decline in value and negatively impact the Portfolio, particularly if changes in prevailing interest rates are more frequent or sudden than the rate changes for the FRNs, which only occur periodically (see “Variable and Floating Rate Instruments” below).

VARIABLE AND FLOATING RATE INSTRUMENTS (principal risk for the Portfolio). Variable and floating rate instruments have interest rates that periodically are adjusted either at set intervals or that float at a margin tied to a specified index rate. These instruments include floating rate Treasury obligations, variable amount master demand notes and long-term variable and floating rate bonds (sometimes referred to as “Put Bonds”) where the Portfolio obtains at the time of purchase the right to put the bond back to the issuer or a third party at par at a specified date.

INVESTMENT STRATEGY. The Portfolio may invest in variable or floating rate instruments to the extent consistent with its investment objective and strategies.

SPECIAL RISKS. Variable and floating rate instruments are subject to many of the same risks as fixed rate instruments, particularly credit risk and default risk, which could impede their value. Because there is no active secondary market for certain variable and floating rate instruments, they may be more difficult to sell if the issuer defaults on its payment obligations or during periods when the Portfolio is not entitled to exercise their demand rights. As a result, the Portfolio could suffer a loss with respect to these instruments. In addition, variable and floating rate instruments are subject to changes in value based on changes in market interest rates or changes in the issuer’s or guarantor’s creditworthiness. In addition, there may be a lag between an actual change in the underlying interest rate benchmark and the reset time for an interest payment of a variable or floating instrument, which could harm or benefit a Portfolio, depending on the interest rate environment or other circumstances. In a rising interest rate environment, for example, a floating or variable rate instrument that does not reset immediately would prevent a Portfolio from taking full advantage of rising interest rates in a timely manner.

In 2017, the FCA warned that LIBOR may cease to be available or appropriate for use by 2021. The unavailability or replacement of LIBOR may affect the value, liquidity or return on certain Portfolio investments and may result in costs incurred in connection with closing out positions and entering into new trades. Any pricing or adjustments to the Portfolio’s investments resulting from a substitute reference rate may adversely affect the Portfolio’s performance and/or NAV (see “LIBOR Transition” above).

WHEN-ISSUED SECURITIES, DELAYED DELIVERY TRANSACTIONS

AND FORWARD COMMITMENTS. A purchase of “when-issued” securities refers to a transaction made conditionally because the securities, although authorized, have not yet been issued. A delayed delivery or forward commitment transaction involves a contract to purchase or sell securities for a fixed price at a future date beyond the customary settlement period.

INVESTMENT STRATEGY. The Portfolio may purchase or sell securities on a when-issued, delayed delivery or forward commitment basis. Although the Portfolio generally would purchase securities in these transactions with the intention of acquiring the securities, the Portfolio may dispose of such securities prior to settlement if the Investment Adviser deems it appropriate to do so.

SPECIAL RISKS. Purchasing securities on a when-issued, delayed delivery or forward commitment basis involves the risk that the value of the securities may decrease by the time they actually are issued or delivered. Conversely, selling securities in these transactions involves the risk that the value of the securities may increase by the time they actually are issued or delivered. Therefore, these transactions may have a leveraging effect on a Portfolio, making the value of an investment in the Portfolio more volatile and increasing the Portfolio’s overall investment exposure. These transactions also involve the risk that the counterparty may fail to deliver the security or cash on the settlement date. If this occurs, the Portfolio may lose both the investment opportunity for the assets it set aside to pay for the security and any gain in the security’s price.

OTHER SECURITIES. Additionally, the Portfolio may purchase other types of securities or instruments similar to those described in these sections if otherwise consistent with the Portfolio’s investment objective and strategies. You should carefully consider the risks discussed in these sections before investing in the Portfolio.

The Portfolio may invest in other securities and is subject to further restrictions and risks that are described in the SAI. Additional information about the Portfolio, its investments and related risks can also be found in “Investment Objective and Strategies” in the SAI.

U.S. Government Select Portfolio 28 Northern Institutional Funds Prospectus

U.S. Government Select Portfolio–Siebert Williams shank Shares

Financial Highlights

THE FINANCIAL HIGHLIGHTS TABLE is INTENDED TO HELP YOU UNDERSTAND THE FINANCIAL PERFORMANCE OF the PORTFOLIO’S siebert WILLIAMS shank SHARES (Formerly, williams capital shares) FOR THE PAST FIVE years.

Certain information reflects the financial results for a single Siebert Williams Shank Share. The total returns in the table represent the rate that an investor would have earned (or lost) on an investment in Siebert Williams Shank Shares of the Portfolio held for the entire period (assuming reinvestment of all dividends and distributions). The information for the fiscal year ended November 30, 2020 has been derived from financial statements that have been audited by Deloitte & Touche LLP, an independent registered public accounting firm, whose reports, along with the Portfolio’s financial statements, are incorporated by reference into this Prospectus and included in the Portfolio’s annual report. Information for fiscal years prior to November 30, 2017 was audited by the Portfolio’s former independent registered public accounting firm. The Portfolio’s annual report, which is available upon request and without charge by calling 800-637-1380, is also available on the Trust’s website at https://www.northerntrust.com/united-states/what-we-do/investment-management/northern-funds/funds-and-performance-institutional/literature or by following the hyperlink: https://www.sec.gov/Archives/edgar/data/710124/000119312521030333/d106269dncsr.htm .

Northern Institutional Funds Prospectus 29 U.S. Government Select Portfolio

U.S. Government Select Portfolio–Siebert Williams shank Shares

Financial Highlightsfor the fiscal years ended november 30,

U.S. Government Select Portfolio	WILLIAMS CAPITAL
Selected per share data	2020	2019	2018	2017	2016
Net Asset Value, Beginning of Year	$1.00	$1.00	$1.00	$1.00	$1.00
INCOME (LOSS) FROM INVESTMENT OPERATIONS:
Net investment income	0.01	0.02	0.02	0.01	—(1)
Net realized gains (losses)(1)	—	—	—	—	—
Total from Investment Operations	0.01	0.02	0.02	0.01	—
LESS DISTRIBUTIONS PAID:
From net investment income	(0.01)	(0.02)	(0.02)	(0.01)	—(1)
From net realized gains	—	—(1)	—(1)	—	—
Total Distributions Paid	(0.01)	(0.02)	(0.02)	(0.01)	—
Net Asset Value, End of Year	$1.00	$1.00	$1.00	$1.00	$1.00
Total Return(2)	0.53%(3)	2.13%	1.58%	0.66%	0.20%
SUPPLEMENTAL DATA AND RATIOS:
Net assets, in thousands, end of period	$1,564,088	$455,839	$216,367	$472,479	$474,161
Ratio to average net assets of:
Expenses, net of waivers, reimbursements and credits	0.18%	0.20%	0.20%(4)	0.20%(4)	0.20%(4)
Expenses, before waivers, reimbursements and credits	0.21%	0.21%	0.21%	0.21%	0.21%
Net investment income, net of waivers, reimbursements and credits	0.25%	2.06%	1.54%(4)	0.66%(4)	0.21%(4)
Net investment income, before waivers, reimbursements and credits	0.22%	2.05%	1.53%	0.65%	0.20%

(1)	Per share amounts from net investment income, net realized gains (losses) and distributions paid from net investment income and net realized gains were less than $0.01 per share.
(2)	Assumes investment at net asset value at the beginning of the year, reinvestment of all dividends and distributions, and a complete redemption of the investment at net asset value at the end of the year.
(3)	Northern Trust Investments, Inc. voluntarily reimbursed expenses of the Williams Capital class of the Portfolio in the amount of approximately $324,000. Total return excluding the voluntary reimbursement would have been 0.51% (see Note 4).
(4)	The impact on Net Assets due to any custody credits is less than 0.005%.

U.S. Government Select Portfolio 30 Northern Institutional Funds Prospectus

Siebert Williams Shank & Co., LLC
100 Wall Street, 18th Floor
New York, NY 10005
Siebertwilliams.com

ANNUAL/SEMIANNUAL REPORTS AND STATEMENT OF ADDITIONAL INFORMATION (“SAI”)

Additional information about the Portfolio’s investments is available in the Portfolio’s annual and semiannual reports to shareholders. In the Portfolio’s annual reports, you will find a discussion of the market conditions and investment strategies that significantly affected the Portfolio’s performance during the last fiscal year.

Additional information about the Portfolio and its policies is also available in the SAI. The SAI is incorporated by reference into this Prospectus (and is legally considered part of this Prospectus).

The Portfolio’s annual and semiannual reports and the SAI are available free upon request by calling the Northern Institutional Funds Center at 800-637-1380 or by sending an e-mail request to: northern-funds@ntrs.com. The SAI and other information are available from a financial intermediary (such as a broker-dealer or bank) through which the Portfolio’s shares may be purchased or sold.

FOR SHAREHOLDER INQUIRIES OR TO OBTAIN INFORMATION:

BY TELEPHONE

For Orders: 800-637-1380

For Questions: 866-926-3863

BY MAIL

Northern Institutional Funds
P.O. Box 75986

Chicago, Illinois 60675-5986

ON THE INTERNET

The Portfolio’s documents are available online and may be downloaded from:

▪

The EDGAR database on the SEC’s web site at sec.gov (text only)

▪

Northern Institutional Funds website at northerntrust.com/institutional

Reports and other information about Northern Institutional Funds are available on the Edgar database on the SEC’s internet site at http://www.sec.gov. You may also obtain copies of Northern Institutional Funds documents, after paying a duplicating fee, by sending your electronic request to: publicinfo@sec.gov.

811-03605

NIF PRO SWS (4/21)

3	Portfolio Summary
	3	U.S. Government Select Portfolio
7	Investment Adviser
8	Management Fees
9	OTHER PORTFOLIO SERVICES
10	PURCHASING AND SELLING siebert WILLIAMS shank SHARES
	10	SHARE CLASSES
	10	PURCHASING Siebert Williams Shank SHARES
	10	OPENING AN ACCOUNT
	11	SELLING Siebert Williams Shank SHARES
12	ACCOUNT POLICIES AND OTHER INFORMATION
17	Distributions AND TAX CONSIDERATIONS
19	SECURITIES, TECHNIQUES AND RISKS
	19	ADDITIONAL INFORMATION ON INVESTMENT OBJECTIVE, PRINCIPAL INVESTMENT STRATEGIES AND RELATED RISKS, DESCRIPTION OF SECURITIES AND COMMON INVESTMENT TECHNIQUES
29	Financial Highlights