Southern Illinois Southern Illinois Southern Illinois (also known as "Little Egypt") is the southern third of the state of Illinois. The southern part of Illinois has a unique cultural and regional history. Part of downstate Illinois, the Southern Illinois region is bordered by the two most voluminous rivers in the United States: the Mississippi River and its connecting Missouri River to the west, and the Ohio River to the east and south with the Wabash as tributary. Southern Illinois' most populated city is Belleville at 44,478. Other principal cities include Alton, Centralia, Collinsville, Edwardsville, Effingham, O'Fallon, Harrisburg, Herrin, Mt. Vernon, Marion, and
Little Wabash River counties, about southeast of New Haven. In its upper course in Shelby County, the river is dammed to form Lake Mattoon and collects the short West Branch Little Wabash River, which flows for its entire length in Shelby County. Other tributaries include the Fox River, which joins it in Edwards County; the Elm River, which joins it in Wayne County; and the Skillet Fork, which joins it in White County. Little Wabash River The Little Wabash River is a tributary of the Wabash River in east-central and southeastern Illinois in the United States. Via the Wabash and Ohio rivers, it