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) in Illinois. Access to a stretch of river around a dam owned by Buzzi Unicem was temporarily barred in 2009 after two drowning deaths that occurred on June 23 and 26, respectively, as well as numerous other boating accidents. The river access was reopened in 2010. The following cities and towns are drained by the Vermilion: The following counties are drained at least in part by the Vermilion 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