River - Illinois
The Illinois River, a tributary of the Mississippi River, is located in central and northern Illinois. It is 273 miles in length and has a drainage area of 28,906 square miles. The Illinois River Basin covers 44 percent of the state, and 90% of Illinois’ population resides in the counties overlapping wholly or partially with the watershed. Its major tributaries include the Macoupin, La Moine, Sangamon, Spoon, Mackinaw, Vermilion, Fox, Des Plaines, and Kankakee Rivers. The main stem of the Illinois River originates at the confluence of the Kankakee and Des Plaines Rivers in Grundy County. The river flows southwest across the state and drains to the Mississippi River near the city of Grafton.