| Sacramento Geckos | USL Second Division | Sacramento | 1997 | — |
| Sacramento Gold FC | National Premier Soccer League | — | 2009 | — |
| Sacramento Knights | Continental Indoor Soccer League | — | 1993 | ARCO Arena |
| Sacramento Knights | National Premier Soccer League | — | 2003 | Folsom High School |
| Sacramento Republic FC | USL Championship | Sacramento | 3 December 2012 | Heart Health Park |
| Sacramento Surge | Major Arena Soccer League | — | 2012 | — |
| Saint Louis FC | USL Championship | St. Louis | 1 May 2014 | World Wide Technology Soccer Park |
| Salem City FC | USL League Two | Greensboro | 1993 | Macpherson Stadium |
| Salinas Valley Samba | National Premier Soccer League | — | 2004 | Watsonville High School |
| Salt Lake Sting | American Professional Soccer League | — | 1990 | Derks Field |
| San Antonio FC | USL Championship | — | 7 January 2016 | Toyota Field |
| San Antonio Pumas | — | — | 1988 | — |
| San Antonio Scorpions | North American Soccer League | — | 2010 | Toyota Field |
| San Diego 1904 FC | National Independent Soccer Association | San Diego | 2017 | Torero Stadium |
| San Diego FC | Major League Soccer | San Diego | 18 May 2023 | Snapdragon Stadium |
| San Diego Flash | A-League, National Premier Soccer League | San Diego | 1998 | Mira Mesa Senior High School |
| San Diego Gauchos | USL League Two | — | 2002 | Torero Stadium |
| San Diego Pumitas | National Premier Soccer League | — | 1999 | Balboa Stadium |
| San Diego Sockers | North American Soccer League | San Diego | 1978 | San Diego Stadium |
| San Diego Sockers | Major Arena Soccer League | San Diego | 2009 | Pechanga Arena |
| San Diego Sockers 2 | — | — | 2017 | Pechanga Arena |
| San Diego Spirit | Women's United Soccer Association | San Diego | 2001 | Torero Stadium |
| San Diego Surf | Premier Arena Soccer League | — | 1980 | — |
| San Diego Toros | North American Soccer League | San Diego | 1966 | Balboa Stadium |
| San Diego Zest FC | USL League Two | San Diego | 2016 | RIMAC Sports Complex |
| San Fernando Valley Quakes | USL League Two | Calabasas | 2006 | — |
| San Francisco Bay Blackhawks | — | — | 1989 | CEFCU Stadium |
| San Francisco Bay Diablos | — | San Francisco | 1993 | — |
| San Francisco City FC | USL League Two | San Francisco | 2001 | Negoesco Stadium |
| San Francisco Deltas | North American Soccer League | San Francisco | 2016 | Kezar Stadium |
| San Francisco Fog | — | — | 1980 | Cow Palace |
| San Francisco Glens | USL League Two | San Francisco | 1961 | Boxer Stadium |
| San Francisco Golden Gate Gales | — | San Francisco | 1967 | Candlestick Park |
| San Francisco Nighthawks | Women's Premier Soccer League | San Francisco | 1995 | Kezar Stadium |
| San Francisco Seals | A-League | San Francisco | 1992 | Negoesco Stadium |
| San Francisco Stompers FC | National Premier Soccer League | Hayward | 2012 | Pioneer Stadium |
| San Francisco Vikings Soccer Club | — | San Francisco | 1922 | — |
| San Gabriel Valley Highlanders | USL League Two | Glendale | 1997 | — |
| San Jose CyberRays | Women's United Soccer Association | San Jose | 2001 | CEFCU Stadium |
| San Jose Earthquakes | North American Soccer League | San Jose | 11 December 1973 | — |
| San Jose Earthquakes U23 | USL League Two | — | 2013 | — |
| San Jose Frogs | USL League Two | San Jose | 2005 | — |
| San Jose Grizzlies | Continental Indoor Soccer League | — | 1993 | SAP Center |
| San Juan United | Liga Nacional de Fútbol de Puerto Rico | — | 2008 | — |
| Santa Ana Winds FC | National Premier Soccer League | Santa Ana | 2009 | Santa Ana Stadium |
| Santa Barbara Condors | — | Santa Barbara | 1977 | — |
| Santa Barbara Sky FC | — | Santa Barbara | 2022 | — |
| Santa Cruz County Breakers | National Premier Soccer League | Santa Cruz | 2007 | — |
| Sarasota Paradise | USL League One | Lakewood Ranch | 19 November 2022 | — |
| Saturn FC | National Premier Soccer League | — | 2009 | — |
| SC United Bantams | USL League Two | Columbia | 2011 | — |
| SD United | Women's Premier Soccer League | — | 2007 | Torero Stadium |
| Seacoast United Mariners | National Premier Soccer League | — | 2011 | Fitzpatrick Stadium |
| Seacoast United Phantoms | USL League Two | Portsmouth | 1996 | — |
| Seacoast United Phantoms | National Premier Soccer League | Portsmouth | 2010 | Portsmouth High School |
| Seattle Impact | Major Arena Soccer League | — | 2014 | accesso ShoWare Center |
| Seattle SeaDogs | Continental Indoor Soccer League | — | November 1993 | Mercer Arena, Climate Pledge Arena |
| Seattle Sounders | North American Soccer League | Seattle | 11 December 1973 | Memorial Stadium |
| Seattle Sounders | USL First Division, A-League | — | 1994 | Starfire Sports |
| Seattle Sounders FC | Major League Soccer | Seattle | 2009 | Lumen Field |
| Seattle Storm | Western Soccer Alliance | — | 1984 | Memorial Stadium |
| Sevilla FC Puerto Rico | Liga Nacional de Fútbol de Puerto Rico | Juncos | 2006 | Juan Ramón Loubriel Stadium |
| Shawsheen Indians | — | Andover | 1923 | — |
| Shreveport Rafters FC | National Premier Soccer League | Shreveport | 2016 | Independence Stadium |
| Sioux Falls Thunder FC | National Premier Soccer League | — | 2016 | — |
| SoCal SC | — | San Bernardino | 2015 | — |
| SoCal Surf | USL League Two | Carlsbad | 2015 | Army and Navy Academy |
| Sonoma County Sol | National Premier Soccer League | Santa Rosa | 2004 | Casa Grande High School |
| Sonoma County Sol | Women's Premier Soccer League | — | 2005 | — |
| Sound FC | USL League Two | Sumner | 2006 | — |
| Southern California Fusion | National Premier Soccer League | Carlsbad | 2004 | — |
| Southern California Lazers | American Soccer League | Torrance | 1978 | — |
| Southern California Seahorses | USL League Two | La Mirada | 2001 | — |
| Southern Colorado Stars | Premier Arena Soccer League | — | 2007 | Colorado Sports Center |
| Southern Oregon Fuego | National Premier Soccer League | — | 2009 | US Cellular Community Park |
| Spartans FC Puerto Rico | Liga Nacional de Fútbol de Puerto Rico | — | 2008 | — |
| Spokane Black Widows | Women's Premier Soccer League | — | 2010 | Joe Albi Stadium |
| Spokane Shadow | USL League Two | Spokane | 1996 | Joe Albi Stadium |
| Spokane Spiders | USL League Two | — | 2006 | Joe Albi Stadium |
| Spokane Velocity | USL League One | Spokane | 2021 | — |
| Sporting Arizona | National Premier Soccer League | Arizona | 1989 | — |
| Sporting Club Jacksonville | — | — | 30 August 2022 | — |
| Sporting Club Jacksonville men | USL Championship | — | 30 August 2022 | — |
| Sporting Club Jacksonville women | USL Super League | — | 16 May 2023 | — |
| Springfield Demize | USL League Two | Springfield | 2006 | — |
| Springfield Storm | USL League Two | — | 2005 | — |
| St. Louis Busch Seniors | — | St. Louis | 1970 | — |
| St. Louis City SC | Major League Soccer | St. Louis | 20 August 2019 | Energizer Park |
| St. Louis Illusion | Major Arena Soccer League | — | 2008 | — |
| St. Louis Knights | — | St. Louis | 1994 | — |
| St. Louis Kutis S.C. | — | St. Louis | 1947 | — |
| St. Louis Lions | USL League Two | St. Louis | 2006 | — |
| St. Louis Simpkins-Ford | — | St. Louis | 1947 | — |
| St. Louis Stars | National Professional Soccer League | St. Louis | 1966 | Busch Memorial Stadium |
| St. Louis Steamers | Major Indoor Soccer League | St. Louis | 1979 | St. Louis Arena |
| St. Louis Steamers | World Indoor Soccer League | — | 1998 | Enterprise Center |
| St. Louis Storm | Major Indoor Soccer League | — | 13 July 1989 | — |
| St. Petersburg FC | USL League Two | St. Petersburg | — | — |
| Stade Brestois New York | — | Queensbridge | 2011 | — |
| Staten Island Vipers | A-League | Staten Island | 1998 | Tottenville High School |
| Stix, Baer and Fuller F.C. | — | St. Louis | 1929 | — |
| Strykers F.C. | Guam Men's Soccer League | Tamuning | — | — |
| Stumptown AC | National Independent Soccer Association | Matthews | 2018 | Sportsplex at Matthews |
| SW Florida Adrenaline | USL League Two | — | 2012 | Estero High School |
| Syracuse FC | National Premier Soccer League | Syracuse | 2017 | — |
| Syracuse Salty Dogs | A-League | — | 2003 | Alliance Bank Stadium |
| Syracuse Suns | — | Syracuse | 1969 | — |