There are two rivers named Illinois River: One in the US state of Illinois and one which runs through parts of Arkansas and Oklahoma.

Illinois River in Illinois

The Illinois River which runs through the state of Illinois begins as the junction of the Kankakee River and the Des Plaines River and runs 273 miles until it reaches the Mississippi River at Grafton, Illinois. It and its tributaries have a drainage basin of 40,000 square miles.

The Illinois River forms part of a waterway that connects the Great Lakes at Chicago to the Mississippi River. The waterway was originally established by the building of the Illinois and Michigan Canal which connected the Illinois River to the Chicago River. When the Chicago River was later reversed the pollution and sewage of the city of Chicago flowed down into the Illinois River. The Illinois and Michigan Canal has since been replaced by the Illinois Waterway and the Sanitary and Ship Canal. The Illinois River is controlled by five lock and dams to facilitate river traffic. The waterway is heavily trafficked by barges transporting bulk goods such as grain and oil.

The Illinois River valley was one of the strongholds of the Illini confederation of Native Americans. The French first met the natives here in 1673. The first European settlement in the state of Illinois was the Jesuit mission founded by Father Jacques Marquette on the banks of the Illinois River at Starved Rock in 1675. In 1680, Robert Cavelier de La Salle built the first fort in Illinois along the river at the present site of Peoria, Illinois where the Jesuits later relocated.

From 1905 to 1915, more freshwater fish were harvested from the Illinois River than from any other river in the U.S., except for the Columbia River. The river was once a major source of mussels for the shell button industry. Overfishing, habitat loss and pollution have eliminated most commercial fishing except for a small mussel harvest to provide shells to seed pearl oysters overseas. The river is still an important sports fishing resource.

Major tributaries of the Illinois are the Kankakee River, Des Plaines River, Fox River, Vermillion River, Spoon River, Sangamon River, La Moine River and the Mackinaw River.

Illinois River in Arkansas and Oklahoma

The Illinois River of Arkansas and Oklahoma is a tributary of the Arkansas River and is about 100 miles long. Together with its tributary streams, it has a drainage area of 900 square miles. Its upper section is a designated scenic river and its lower section is a designated trout stream. The middle section consists of Tenkiller Lake. The town of Tahlequah, Oklahoma on its banks was the western terminus of the Trail of Tears.

The Illinois River is a major source of tourism in the area. In 1999, it was estimated to bring in 500,000 tourists and $9 million dollars to the Oklahoma section of the river.

The river is currently the source of a controversy between the two states, with Oklahoma blaming Arkansas for polluting the river, mainly by sewage and poultry farm runoff.