The Interstate League was the name of five different American minor baseball leagues that played intermittently from 1896 through 1952. The longest tenured of these was the last incarnation, which played in the Middle Atlantic States from 1939 through 1952, and was one of the few mid-level minor leagues to operate continuously during the World War II period.
This circuit, which began as Class C and was upgraded to Class B in 1940, typically had teams in Allentown, Harrisburg, Lancaster and Sunbury, all in Pennsylvania; Hagerstown, Maryland; Trenton, New Jersey; and Wilmington, Delaware. Its final champion was the Hagerstown Braves, a Boston Braves affiliate. That season, the York White Roses led the league in attendance, attracting over 78,000 fans.
Earlier versions of the Interstate League, with years active:
In addition, a Class C Interstate Association existed for one season, 1906, in Michigan, Indiana and Ohio.

1896-1901: an unclassified loop with teams in Ohio, Indiana, Michigan, Kentucky, and West Virginia.
1905-08; 1914-16: a Class D league with clubs in Pennsylvania and New York.
1913: a Class C league operating in Ohio, Pennsylvania and West Virginia.
1932: a Class D circuit based in Pennsylvania and New Jersey.