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) these as a single river that flowed in two directions. It is also possible that, in early settlement times, these rivers formed a canoe route between the Illinois River and Wabash River, with a portage through the marshes near Roberts. This may explain why the two rivers have the same name. The north-flowing Vermilion flows in a northerly direction from its origin in Livingston and Ford counties in north central Illinois, eventually emptying into the Illinois River, near Oglesby. Perhaps it is best known for its stretch of whitewater between Lowell and Oglesby, Illinois, which is one of few found