The Rock Island Islanders was the primary name of the minor league baseball teams based in Rock Island, Illinois, one of the Quad Cities, between 1892 and 1937. Rock Island teams played as members of the Illinois–Iowa League (1892), Western Association (1894), Eastern Iowa League (1895), Western Association (1898–1899), Illinois–Indiana–Iowa League (1901–1911), Central Association (1914), Illinois–Indiana–Iowa League, Mississippi Valley League (1922–1933) and Western League (1934–1937).

The Rockford Rox was the primary moniker of the minor league baseball teams based in Rockford, Illinois, between 1871 and 1949. In an era of early baseball, Rockford hosted teams in numerous leagues beginning in 1871. From 1916 to 1923, the Rox played in the Class B level Illinois–Indiana–Iowa League, and from 1947 to 1949, they played in the Class C level Central Association. The Rockford Rox were preceded by the Rockford Red Sox (1901–1904) and Rockford Wakes (1914–1916) in the Illinois–Indiana–Iowa League. Several other Rockford teams played in various leagues leading up to the Rox. The Rockford Rox were an affiliate of the Cincinnati Reds from 1947 to 1949.