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 (Little Wabash tributary) Fox River: Fox River (Little Wabash tributary) The Fox River is a tributary of the Little Wabash River in southern Illinois. It rises in Jasper County to the southeast of Newton and flows south past Olney, then joins the Little Wabash at the northeast corner of Edwards County, near Mt. Erie. The river is in length. There is a smaller "Fox River" that is a tributary of the Wabash River in southern Illinois, entering the Wabash near New Harmony, Indiana. The following cities, towns and villages are in the Fox River watershed: The following counties are at least partially drained