American soccer writing, history & data.
| Club | Location | Years |
|---|---|---|
| Oakland Clippers | - | 1967–1968 |
| Oakland F.C. | - | 1910–1911 |
| Oakland Roots Sports Club | - | 2019 |
| O'Brien Live Wires | - | 1912–1913 |
| Occidental A.C. | - | 1903–1905 |
| Ocean City Nor'easters | - | 1997 |
| Oertli Markets | - | 1935–1936 |
| Ohio XOGGZ | - | 1994–1998 |
| Okanagan Challenge S.C. | - | 1990–2012 |
| Oklahoma City Hatters | - | 1998–1998 |
| Oklahoma City Heat | - | 1996–1996 |
| Oklahoma City Slickers | - | 1982–1983 |
| Oklahoma City Spirit S.C. | - | 1990 |
| Oklahoma City Warriors | - | 1986–1998 |
| Oklahoma City Wind | - | 1999–1999 |
| O'Learys | - | 1907–1912 |
| Olympia S.C. | - | 1965–1967 |
| Olympic Club | - | 1914–1921 |
| Omaha Flames | - | 1996–1998 |
| Orange County Blue Star | - | 1997–2012 |
| Orlando City U-23 | - | 1998–2015 |
| Orlando Lions | - | 1992–1996 |
| Orlando Lions S.C. | - | 1986–1990 |
| Orlando Nighthawks | - | 1997–1999 |
| Orlando Sundogs | - | 1997–1997 |
| Oscar Mayer Co. | - | 1934–1936 |
| Oshkosh Sport Club | - | 1927–1964 |