|Most titles||10 Duluth/Duluth-Superior|
The Northern League name represented four leagues in this time frame:
In 1906, the league merged with the Copper Country Soo League to become the Northern-Copper Country League (1906-1907). A second Northern League was attempted in 1908, but did not finish its first season. The third Northern League appeared when the Central International League of 1912 expanded and changed its name in 1913. This third Northern League would last until 1917, when it was forced to disband due to a lack of players as a result of World War I.
The league did not re-emerge until 1933, when it began play with the Brainerd Muskies, Brandon Grays, Crookston Pirates, East Grand Forks Colts, Eau Claire Cardinals, Fargo-Moorhead Twins, Superior Blues and Winnipeg Maroons. The league did not operate between 1943 and 1945 because of a lack of manpower during World War II, and finally folded again in 1971.
While the Northern League in its various incarnations began as an independent loop in 1902, it was Class D (1903–1905, 1908, 1917, 1933–1940) and Class C (1913–1916, 1941–1942, 1946–1962) under the antiquated classification system for Minor League Baseball. The league operated as Class A (1963-1971) under the modern minor league classification system. When the league folded after the 1971 season, the remaining teams were the Aberdeen Pheasants, Sioux Falls Packers, St. Cloud Rox and Watertown Expos.