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
Muddy River (Massachusetts) of the Muddy River into the tidal Charles was much wider. It formed the eastern Brookline border with Boston and Roxbury (depending on the year), from Brookline's incorporation in 1705 until Boston's annexation of Allston–Brighton in 1873. The present form of the river and surrounding parks was created by the Emerald Necklace project, between 1880 and 1900. Under the direction of designer Frederick Law Olmsted, the project reclaimed marshland, creating sculpted and planted riverbanks. The Muddy River is mentioned by John Winthrop, in his famous "Journal of John Winthrop," as the site of an unidentified flying object in March 1638