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
Course of the Colorado River colorful and intricately sculpted rock formations. The Escalante River, a desert stream which runs through the sinuous slot canyons of Grand Staircase-Escalante National Monument, joins about two-thirds of the way down Lake Powell. The San Juan River, which carries runoff from the southern slopes of the San Juan Mountains and the Four Corners region in Colorado and New Mexico, joins several miles further downstream; it forms an arm of the lake nearly long. Although the San Juan contributes only about one-tenth of the Colorado River flow, it is extremely muddy, contributing as much as 40 percent of the total sediment