Illinois (river)

Illinois (river), river in northern Illinois, an important tributary of the upper Mississippi River, crossing the state from a point southwest of Chicago to a point on the Mississippi above Alton, Illinois. It is formed by the union of the Des Plaines and Kankakee rivers in the northeast and flows in a generally southwestern direction for a total distance of 680 km (420 mi). The drainage area of the river is 75,000 sq km (29,000 sq mi), of which 64,000 sq km (25,000 sq mi) lie in Illinois and the remainder in Indiana and Wisconsin. The Illinois is broad and deep.

As part of the historic Illinois and Michigan Canal, completed in 1848, the Illinois River played a major role in the development of northern Illinois and Chicago. The canal extended from the Illinois River at La Salle, Illinois, to the Chicago River. As part of the canal, the Illinois provided a vital link between the Mississippi River and Lake Michigan. The canal ceased to be used in 1900. Today the Illinois is part of the Illinois Waterway, a system of rivers and canals that provides uninterrupted passage between the Great Lakes and the Mississippi. The Illinois has a large number of tributaries, the most important of which are the Fox and Sangamon rivers. The principal cities on the banks of the river are Ottawa, Illinois; and Peoria, Illinois.