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
Vermilion River (Illinois River) Vermilion River (Illinois River) The Vermilion River is a tributary of the Illinois River in the state of Illinois, United States. The river flows north, in contrast to a second Vermilion River in Illinois, which flows south to the Wabash River. The Illinois and Wabash rivers each have a tributary named the Little Vermilion River as well. The north-flowing Vermilion River and the south-flowing Middle Fork Vermilion River run on what is close to a straight line between Oglesby and Danville. In presettlement times, the two rivers drained an upland marsh near Roberts. It is possible that early settlers regarded