Lake Glenn Shoals is a 1,250 acres reservoir located in Montgomery County, Illinois. Created in 1976 by damming the Middle Fork of Illinois's Shoal Creek, it was built for recreation, sport fishing, and water supply purposes. The lake is 4 miles long and 0.4 miles wide. The nearest town is Hillsboro, Illinois, south of Springfield, Illinois and northeast of Saint L…Lake Glenn Shoals is a 1,250 acres reservoir located in Montgomery County, Illinois. Created in 1976 by damming the Middle Fork of Illinois's Shoal Creek, it was built for recreation, sport fishing, and water supply purposes. The lake is 4 miles long and 0.4 miles wide. The nearest town is Hillsboro, Illinois, south of Springfield, Illinois and northeast of Saint Louis, Missouri.