Form 497 STATE STREET INSTITUTION

STATE STREET INSTITUTIONAL FUNDS

State Street Institutional U.S. Equity Fund

(the “Fund”)

Supplement dated April 12, 2019 to the Summary Prospectus, Prospectus and

Statement of Additional Information (“SAI”) each dated January 31, 2019,

each as may be revised and/or supplemented from time to time.

Effective August 30, 2019 (the “Effective Date”), Michael Solecki will replace David Carlson as a Portfolio Manager on the Fund. Accordingly, as of the Effective Date, the Prospectus, Summary Prospectus and SAI will be revised as follows:

PORTFOLIO MANAGEMENT

INVESTMENT ADVISER

SSGA Funds Management, Inc. (“SSGA FM” or the “Adviser”)

PORTFOLIO MANAGERS

The primary individual portfolio managers of the Fund are:

The State Street Institutional U.S. Equity Fund is managed by a team of portfolio managers that includes Michael Solecki, Paul Nestro and Christopher Sierakowski. Mr. Nestro manages one of two sub-portfolios that comprise the Fund, while Mr. Sierakowski manages the other sub-portfolio. A sub-portfolio refers to the portion of the Fund’s assets that are allocated to, and managed (or co-managed) by, a particular portfolio manager on the Fund’s portfolio management team. One portfolio, run by Mr. Nestro, seeks to own the best ideas from the research analyst team with about 130 names and stays close to sector neutral. The other portfolio, run by Mr. Sierakowski, looks to concentrate those best ideas to only 30-40 securities and takes sector bets. The current allocation between the two sub-portfolios is 70/30 based on the desired combined portfolio characteristics and can be adjusted over time by Mr. Solecki. The two sub-portfolios are managed independently of each other and the portfolio managers have full discretion over their respective sub-portfolios.

Michael Solecki, CFA, is a Senior Managing Director of SSGA and the Adviser, Portfolio Manager and Chief Investment Officer for Fundamental Growth and Core Equity. He is also a member of SSGA’s Executive

Management Group. Previously, Mr. Solecki was Chief Investment Officer for Fundamental International Equities. He joined SSGA in July 2016 through its acquisition of GE Asset Management (“GEAM”). Previously at GEAM, as part of the International Equity team, he held roles as Chief Investment Officer, Co-Chief Investment Officer, Director of Portfolio Management and a Director of Research for the International Equity research team. He joined GEAM in 1991 after completing GE’s Financial Management Program where he had financial assignments at GE Energy, GE Capital and GEAM. While at GEAM, Mr. Solecki started as an analyst in International Equities in 1991 responsible for Latin America and Canada. He relocated to GEAM’s London offices in 1992 where he led their European equity research until 1995. Since 1995, Mr. Solecki has managed various equity portfolios and covered a variety of sectors outside the U.S. equity market. Prior to GE, he worked for Monarch Capital Corporation. Mr. Solecki holds a Bachelor of Science in Finance from Western New England College and a Master of Business Administration from Fordham University. He is a holder of the Chartered Financial Analyst designation and is a member of the New York Society of Security Analysts.

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