| Southeastern Louisiana University | public educational institution of the United States, university | — | 1925 |
| Southern California Institute of Architecture | architecture school, private not-for-profit educational institution, university | — | 1972 |
| Southern Illinois University Carbondale | public educational institution of the United States, public university | — | 1869 |
| Soylent | brand, business, drink mix, meal replacement | Los Angeles | 2013 |
| SpaceX | launch service provider, business, public company, aerospace manufacturer | Starbase | March 14, 2002 |
| Spansion | business, enterprise, public company | Sunnyvale | 2003 |
| Specialized Bicycle Components | bicycle manufacturer, business, enterprise | Morgan Hill | 1974 |
| Spector | business | Saugerties | 1976 |
| Spectrum Brands | business, enterprise, public company | Middleton | 1906 |
| Sports Reference | business | Philadelphia | December 3, 2007 |
| Springfield Armory | business | Geneseo | 1974 |
| Sprint Corporation | mobile network operator, business, enterprise, public company | Overland Park | 1899 |
| Squarespace | commercial organization, public company | New York City | 2003 |
| St. Edward's University | private not-for-profit educational institution, university | — | 1873 |
| St. Thomas University | private not-for-profit educational institution, university, open-access publisher | — | 1961 |
| Standard Oil | holding company, business, enterprise | Ohio, Cleveland, New York City | 1890 |
| Stanford University | research university, private not-for-profit educational institution, open-access publisher, private university | Stanford | 1885 |
| Stanley Black & Decker | business, public company | New Britain | 1843 |
| Staples Inc. | business, retail chain, enterprise, public company | Framingham | 1986 |
| Starbucks | café chain | Seattle | March 30, 1971 |
| Starwood | business, enterprise, public company | White Plains | 1930 |
| State Farm Insurance | business, car insurance company, life insurance company, property insurance company | Bloomington | 1922 |
| State University of New York at Albany | public educational institution of the United States, public university | Albany | 1844 |
| State University of New York at Purchase | public educational institution of the United States, university | — | 1967 |
| Steak 'n Shake | restaurant chain, business, enterprise | Indianapolis | 1934 |
| Steinway Musical Instruments | business, musical instrument manufacturing company, enterprise | Waltham | 1995 |
| Sterling Memorial Library | academic library, library building | — | 1930 |
| Sterling Trucks | truck manufacturer, commercial vehicle manufacturer | Redford | 1997 |
| Stevens Institute of Technology | private not-for-profit educational institution, university | — | 1870 |
| Strand Bookstore | book vendor | — | 1927 |
| Stratfor | think tank, business, secret service | Austin | 1996 |
| Stratolaunch Systems | business, enterprise | Montgomery, Seattle | 2011 |
| Stripe | payment processor, business | San Francisco, South San Francisco | 2010 |
| Studebaker | business, automobile manufacturer | South Bend | 1852 |
| Stuyvesant High School | school, specialized high school in New York City, high school | New York City | 1904 |
| STX Entertainment | film production company, film distributor, public company | Burbank | March 10, 2014 |
| Stüssy, Inc. | business, enterprise | Irvine | 1980 |
| Sullivan & Cromwell | law firm | New York City | 1879 |
| Sumisho Air Lease | business, enterprise, public company | Los Angeles | 2010 |
| Sunkist Growers | business, enterprise | Los Angeles | August 29, 1893 |
| Supergiant Games | video game publisher, video game developer | San Jose | 2009 |
| SureFire | business, enterprise | Fountain Valley | 1979 |
| SurveyMonkey | customer experience management, software as a service, service on Internet, trademark, enterprise feedback management, online survey service, market research and public opinion polling, business, Customer experience systems, public company, market research | San Mateo | 1999 |
| Swarthmore College | liberal arts college, private not-for-profit educational institution | — | 1864 |
| Swift Engineering | business, enterprise, aerospace manufacturer | San Clemente | 1983 |
| Synopsys | business, enterprise, public company | Mountain View | 1986 |
| Sysco | business, public company | Houston | 1969 |
| System76 | brand, business | Denver | November 7, 2005 |