There was a class D league called the Wisconsin State League which began in 1905. In 1908 it changed its name to the Wisconsin-Illinois League. Another Wisconsin State League began in 1940, shut down for World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

 from 1943 through 1945, then operated from 1946 through 1953. This was also a class D league, but with the majority of teams being affiliated with the major leagues, quality was likely higher than in many class D leagues.