Illinois River 20 miles (32 km) of its course, the Illinois is separated from the Mississippi River by only about five miles, by a peninsula of land that makes up Calhoun County. The Illinois joins the Mississippi near Grafton, approximately 25 miles (40 km) northwest of downtown St. Louis and about 20 miles upstream from the confluence of the Missouri River and the Mississippi. South of Hennepin, the Illinois River is following the ancient channel of the Mississippi River. The Illinoian Stage, about 300,000 to 132,000 years ago, blocked the Mississippi near Rock Island, diverting it into its present channel. After the
Fox River (Illinois River tributary) Fox River (Illinois River tributary) The Fox River is a tributary of the Illinois River, flowing from southeastern Wisconsin to Ottawa, Illinois in the United States. The Wisconsin section was known as the Pishtaka River in the 19th century. There are two other "Fox Rivers" in southern Illinois: the Fox River (Little Wabash tributary) and a smaller "Fox River" that joins the Wabash River near New Harmony, Indiana. The Fox River rises in the Halbach Swamp, southeast of the community of Colgate, Wisconsin and flows past Brookfield, Waukesha, Big Bend, Waterford, Rochester, Burlington, Wheatland, Silver Lake and Wilmot, for a