Southern Idaho League was an independent league based in Idaho.
1903 Boise, Caldwell, Emmett, Nampa, Payette, Weiser
1905 Boise, Caldwell, Emmett, Nampa, Payette, Weiser
1906 Boise, Caldwell, Nampa, Weiser
1907 No teams entered or left the league.
1908 No teams entered or left the league.
1923 Eden, Hansen, Jerome, Kimberley, Shoshone, Twin Falls
1933 Buhl, Burley, Declo, Filer, Hansen, Hazleton, Kimberley, Paul, Rupert, Twin Falls, Wendel
1934 Gooding, Hurley, and Rockland entered the league; Burley and Twin Falls left the league.