| Six Flags | business, enterprise, public company | Arlington | 1961 |
| Six Flags Great Adventure | animal theme park | — | July 1, 1974 |
| Six Flags Magic Mountain | amusement park | — | 1971 |
| Skadden, Arps, Slate, Meagher & Flom | law firm | 1 Manhattan West | 1948 |
| Skechers | business, enterprise, public company | Manhattan Beach | 1992 |
| Skidmore, Owings and Merrill | architectural firm | Chicago | 1936 |
| Skullcandy | business, public company | Park City | 2003 |
| Sky & Telescope | business, scientific journal | — | 1941 |
| Skybound Entertainment | business | Beverly Hills | 1992 |
| Skydance Direct-to-Consumer | media company | San Francisco | April 12, 2007 |
| Slack Technologies | business, public company | San Francisco | 2009 |
| Sledgehammer Games | video game developer | Foster City | 2009 |
| Slots-A-Fun Casino | casino | — | August 5, 1971 |
| Smashburger | restaurant chain | Denver | 2007 |
| Smith & Wesson | business, enterprise, public company | Springfield | 1852 |
| Smithfield Foods | business, enterprise, public company | Smithfield | 1936 |
| Society for Industrial and Applied Mathematics | mathematical society, nonprofit organization, publishing house, source of information, learned society | University City | 1951 |
| Society of Biblical Literature | organization, open-access publisher, scientific society, learned society | Atlanta | 1880 |
| Society of Petroleum Engineers | engineering society, nonprofit organization, professional association, academic publisher | Richardson, Texas, United States | October 6, 1957 |
| Soka University of America | private not-for-profit educational institution, higher education institution, school | Aliso Viejo | 2001 |
| Sonoma State University | public educational institution of the United States, university, census-designated place in the United States | — | 1960 |
| Sonos | business, enterprise, public company | Santa Barbara | 2002 |
| Sons of the American Revolution | research library, nonprofit organization, patriotic society, museum, men's organization, charitable organization, lineage society | Louisville | April 30, 1889 |
| Sony Corporation of America | business, subsidiary company | 550 Madison Avenue, New York City | 1960 |
| Sony Imagesoft | business | Los Angeles | 1989 |
| Sony Music | major label, record company, business | New York City | January 1, 2009 |
| Sony Pictures Animation | animation studio | Culver City | 2002 |
| Sony Pictures Classics | film production company, film distributor | New York City, Los Angeles | January 1992 |
| Sony Pictures Television | television production company, division | Culver City | September 16, 2002 |
| Soros Fund Management | privately held company | New York City | — |
| SoundHound | music recognition software, enterprise, public company | Santa Clara | September 2005 |
| Southeastern Louisiana University | public educational institution of the United States, university | — | 1925 |
| Southern Air | cargo airline, airline | Norwalk | 1947 |
| Southern California Institute of Architecture | architecture school, private not-for-profit educational institution, university | — | 1972 |
| Southern Company | energy company, business, enterprise, public company | Atlanta | 1945 |
| Southern Connecticut State University | public educational institution of the United States, university | New Haven | 1893 |
| Southern Illinois University | state university system | — | 1869 |
| Southwest Airlines | airline, business, public company | Dallas | 1967 |
| Soylent | brand, business, drink mix, meal replacement | Los Angeles | 2013 |
| SpaceXAI | holding company, business | San Francisco Bay Area | March 9, 2023 |
| Specialized Bicycle Components | bicycle manufacturer, business, enterprise | Morgan Hill | 1974 |
| Spector | business | Saugerties | 1976 |
| Spectrum HoloByte | video game developer | Alameda | 1983 |
| SpinLaunch | launch service provider, space company | Long Beach | October 28, 2014 |
| Splunk Inc. | software company, enterprise, public company | San Francisco | 2004 |
| Springer Publishing | publishing house | New York City | 1950 |
| Springer Science+Business Media | book publisher, publishing house, academic publisher | Luxembourg | May 10, 1842 |
| Springfield Armory | business | Geneseo | 1974 |