| Indiana Blaze | USL W-League | — | 1997 | Kuntz Stadium |
| Indiana Invaders | USL League Two | — | 1998 | Indiana Invaders Soccer Complex |
| Indiana Tigers | — | Gary | 1973 | — |
| Indianapolis Braves | National Premier Soccer League | — | 2007 | — |
| Indianapolis Daredevils | — | Indianapolis | 1974 | — |
| Indios USA | — | — | 2007 | Canutillo Stadium |
| Indy Eleven | USL Championship | Indianapolis | 2013 | IU Michael A. Carroll Track & Soccer Stadium |
| Inter Godfather's | M*League Division 1 | Garapan | 2005 | — |
| Inter Miami CF | Major League Soccer | Miami | 29 January 2018 | Chase Stadium |
| Inter Nashville FC | National Premier Soccer League | Nashville | — | — |
| Isabela Soccer Club | Liga Nacional de Fútbol de Puerto Rico | — | 2011 | — |
| Jackson Chargers | USL League Two | Jackson | 1995 | — |
| Jacksonville Armada FC | North American Soccer League | — | 2013 | VyStar Ballpark |
| Jacksonville Cyclones | A-League | — | 1995 | Mandarin High School |
| Jacksonville Tea Men | North American Soccer League | — | 1980 | Gator Bowl Stadium |
| Jersey City Celtics | American Soccer League | Jersey City | 1921 | — |
| Jersey Express S.C. | USL League Two | Newark | 2007 | Elizabeth High School |
| Jersey Shore Boca | USL League Two | — | 2003 | Ocean County College |
| Kalamazoo FC | National Premier Soccer League | Kalamazoo | 2015 | — |
| Kalamazoo Kingdom | USL League Two | — | 1996 | — |
| Kalamazoo Outrage | USL League Two | — | 2007 | Loy Norrix High School |
| Kansas City Current | National Women's Soccer League | Overland Park | 6 December 2020 | Sporting Park, Legends Field |
| Kansas City Spurs | North American Soccer League | Kansas City | 1967 | Municipal Stadium |
| Kansas Magic | Major Arena Soccer League | — | 2011 | — |
| KC Athletics | United States Adult Soccer Association | — | 2001 | — |
| Kearny Celtic | North Jersey Soccer League | Kearny | 1933 | — |
| Kearny Scots | Eastern Premier Soccer League | Kearny | 1895 | — |
| Keene FC | United Premier Soccer League | — | 2017 | Wanda R. Smith High School |
| Kingston Stockade Football Club | National Premier Soccer League | Kingston | 2015 | Dietz Stadium |
| Kitsap Pumas | USL League Two | Bremerton | 2009 | — |
| Kiwi Soccers | ASFA Soccer League | — | 2010 | National Stadium |
| Knoxville Force | National Premier Soccer League | Knoxville | 2010 | — |
| Kraze United | National Premier Soccer League | — | 2015 | UCF Soccer and Track Complex |
| L.A. Wolves FC | United Premier Soccer League | — | 2014 | — |
| LA Galaxy | Major League Soccer | Los Angeles | 1995 | Dignity Health Sports Park |
| La Máquina FC | United Premier Soccer League | Santa Ana | 2011 | — |
| Lafayette Swamp Cats | USL League Two | — | 2000 | — |
| Lafayette SwampCats | Eastern Indoor Soccer League | — | 1997 | Cajundome |
| Lancaster Inferno | National Premier Soccer League | — | 2008 | Hempfield High School |
| Lansdowne Bhoys FC | Cosmopolitan Soccer League | Yonkers | — | — |
| Laredo Heat | USL League Two | Laredo | 2004 | Texas A&M International University Soccer Complex |
| Laredo Honey Badgers | Major Arena Soccer League | — | 2013 | Laredo Energy Arena |
| Las Vegas Lights FC | USL Championship | Las Vegas | 11 August 2017 | Cashman Field |
| Las Vegas Quicksilvers | North American Soccer League | Las Vegas | 1976 | Sam Boyd Stadium |
| Las Vegas Seagulls | American Soccer League | Las Vegas | 1979 | Sam Boyd Stadium |
| Las Vegas Strikers | National Premier Soccer League | — | 2003 | — |
| Lehigh Valley Steam | A-League | Lehigh Valley | 1999 | — |
| Lexington SC | — | Lexington | 2021 | — |