Northwestern League was an independent league.
1879 Davenport IA, Dubuque IA, Omaha NE, Rockford IL
1881 Unknown
1883 Bay City MI, Ft Wayne IN, Grand Rapids MI, Peoria IL, Quincy IL, Saginaw, MI, Springfield IL, Toledo OH
1884 Milwaukee WI, Minneapolis MN, Muskegon MI, Stillwater MN, St Paul, MN and Terre Haute IN entered the league; Springfield and Toledo left the league. During the season, the Bay City franchise moved to Evansville, IN
1885 Duluth, Mn entered the league; Evansville, Ft Wayne, Grand Rapids, Peoria, Quincy, Saginaw and Terre Haute left the league.
1886 Eau Claire, WI and Oshkosh, Wi entered the league; Muskegon and Stillwater left the league.
1887 Des Moines, IA and LaCrosse WI entered the league.
1891 Bay City MI, Dayton OH, Detroit MI, Evansville IN, Fort Wayne IN, Grand Rapids MI, Peoria IL, Terre Haute IN. Due to severaal franchises withdrawing, three seasons were played. But when Grand Rapids and Terre Haute also withdrew, the season was terminated July 30.
1895 unknown