The Northern League was a name used by several minor league baseball organizations that operated off and on between 1902 and 1971 in the upper midwestern United States and Manitoba, Canada. The name was later used by the independent Northern League from 1993 to 2010.

The Northern League name represented four leagues in this time frame:

• First Northern League: 1902–1905
  • Northern-Copper Country League 1906–1907
• Second Northern League: 1908
  • Minnesota–Wisconsin League 1909–1911
  • Central International League 1912
• Third Northern League: 1913–1917
• Fourth Northern League: 1933–1971 (suspended operations 1943–1945 due to World War II)

The first Northern League operated between 1902 and 1905. Charter members were the Winnipeg Maroons, Crookston Crooks, Fargo, Devil's Lake, Grand Forks and Cavalier.^[1]

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.^[2] 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.^[3] When the league folded after the 1971 season, the remaining teams were the Aberdeen Pheasants, Sioux Falls Packers, St. Cloud Rox and Watertown Expos.^[4]

Source: ^[5]

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• Cavalier, North Dakota: Cavalier 1902 ** Disbanded on July 21, 1902.
• Crookston, Minnesota: Crookston Crooks 1902–1905
• Devils Lake, North Dakota: Devil's Lake 1902 ** Disbanded on July 21, 1902.
• Duluth, Minnesota: Duluth White Sox 1903–1905
• Fargo, North Dakota: Fargo 1902–1905
• Grand Forks, North Dakota: Grand Forks Forkers 1902–1905
• St. Cloud, Minnesota, and Brainerd, Minnesota: St. Cloud-Brainerd 1905 ** Moved to Superior on June 25, 1905.
• Superior, Wisconsin: Superior Longshoremen 1903–1905 ** The first Longshoremen team disbanded August 8, 1903. The third Longshoremen was the relocated St. Cloud-Brainerd franchise, which moved on June 25, 1905.
• Winnipeg, Manitoba: Winnipeg Maroons 1902–1905

^[5]

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• Brandon, Manitoba: Brandon Angels 1908
• Duluth, Minnesota: Duluth White Sox 1908
• Fargo, North Dakota: Fargo Browns 1908
• Winnipeg, Manitoba: Winnipeg Maroons 1908

^[5]

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• Duluth, Minnesota: Duluth White Sox 1913–1916
• Fargo, North Dakota, and Moorhead, Minnesota: Fargo-Moorhead Graingrowers 1914–1917
• Fort William, Ontario: Fort William Canadians 1914–1915
• Fort William, Ontario and Port Arthur, Ontario: Fort William-Port Arthur Canadians 1916 ** Withdrew July 10, 1916.
• Grand Forks, North Dakota: Grand Forks Flickertails 1913–1915
• The team withdrew from the league on July 5, 1915.
• LaCrosse, Wisconsin: LaCrosse Colts 1913 ** Moved from St. Paul July 23, 1913.
• Minneapolis, Minnesota: Minneapolis Millers 1913
• Minot, North Dakota: Minot Why Nots 1917
• St. Boniface, Manitoba: St. Boniface Bonnies 1915
• St. Paul, Minnesota: St. Paul Colts 1913 ** Moved to LaCrosse July 23, 1913.
• Superior, Wisconsin: Superior Red Sox 1913–1915 ** Withdrew July 5, 1915.
• Virginia, Minnesota: Virginia Ore Diggers 1913–1916 ** Withdrew July 10, 1916.
• Warren, Minnesota: Warren Wanderers 1917
• Winnipeg, Manitoba: Winnipeg Maroons 1913–1917
• Winona, Minnesota: Winona Pirates 1913–1914

^[5]

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• Aberdeen, South Dakota: Aberdeen Pheasants 1946–1971
• Bismarck, North Dakota, and Mandan, North Dakota: Bismarck-Mandan Pards 1962–1964; Bismarck-Mandan Pards 1966
• Brainerd, Minnesota, and Little Falls, Minnesota: Brainerd Muskies 1933; Brainerd-Little Falls Muskies 1934; Brainerd Blues 1935
• Brandon, Manitoba: Brandon Grays 1933
• Crookston, Minnesota: Crookston Pirates 1933–1941
• Duluth, Minnesota: Duluth White Sox 1934 Duluth Dukes 1935–1942, 1946–1955
• Duluth, Minnesota, and Superior, Wisconsin: Duluth-Superior White Sox 1956–1959; Duluth–Superior Dukes 1960–1970
• East Grand Forks, Minnesota: East Grand Forks Colts 1933
• Eau Claire, Wisconsin: Eau Claire Cardinals 1933; Eau Claire Bears 1934–1942, 1946–1953; Eau Claire Braves 1954–1962
• Fargo, North Dakota, and Moorhead, Minnesota: Fargo-Moorhead Twins 1933–1942, 1946–1960
• Grand Forks, North Dakota: Grand Forks Chiefs 1934–35; Grand Forks Chiefs 1938–1942, 1946–1963; Grand Forks Dodgers 1964
• Huron, South Dakota: Huron Phillies 1965–1968; Huron Cubs 1969–1970
• Jamestown, North Dakota: Jamestown Jimmies 1936–1937
• Mankato, Minnesota: Mankato Mets 1967–1968
• Minot, North Dakota: Minot Mallards 1958–1960; Minot Mallards 1962
• St. Cloud, Minnesota: St. Cloud Rox 1946–1971
• Sioux Falls, South Dakota: Sioux Falls Canaries 1942, 1946–1953; Sioux Falls Packers 1966–1971
• Superior, Wisconsin: Superior Blues 1933–1942, 1946–1955
• Watertown, South Dakota: Watertown Expos 1970–1971
• Wausau, Wisconsin: Wausau Lumberjacks 1936–1939; Wausau Timberjacks 1940–1942; Wausau Lumberjacks 1956–1957
• Winnipeg, Manitoba: Winnipeg Maroons 1933–1942; Winnipeg Goldeyes 1954–1964; Winnipeg Goldeyes 1969

^[5]

• Ballparkwatch Northern League history
• An Informal History of the Northern League by Herman D. White