Illinois River Facts



The Illinois River valley was one of the strongholds of the Illinois Confederationof Native Americans. The French first met the natives here in 1673. The first European settlement in the state of Illinois was the Jesuitmission founded in 1675 by Father Jacques Marquetteon the banks of the Illinois across from Starved Rockat the Grand Village of the Illinois. In 1680, René-Robert Cavelier, Sieur de La Sallebuilt the first fort in Illinois, Ft. St. Louis, at Starved Rock. Later it was relocated to the present site of Creve Coeur, near Peoria, where the Jesuits relocated.

From 1905 to 1915, more freshwater fish were harvested from the Illinois River than from any other river in the United States except for the Columbia River. The Illinois River was once a major source of mussels for the shell button industry. Overfishing, habitat loss from heavy siltation, and water pollution have eliminated most commercial fishing except for a small mussel harvest to provide shells to seed pearl oysters overseas. It is commercially fished downstream of the Rt. 89 bridge at Spring Valley. The Illinois River is still an important sports fishing waterway with a good sauger fishery.


The Illinois forms part of a modern 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 that connected the Illinois River to the Chicago River. When the Sanitary District of Chicago later reversed the flow of the Chicago River, 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 The Illinois and Michigan Canal has since been replaced by the Illinois Waterway, including the Chicago Sanitary and Ship Canal. River traffic and flood control is managed by eight locks and dams operated by the U.S. Army Corps of Engineers.

As of 2011, all locks and dams on this waterway are closed to visitors for security reasons, except the Starved Rock Visitor Center, which offers an excellent interpretation of the entire system. The waterway is heavily used by barges transporting bulk goods such as grain and oil. It is used in the summer and early fall by tourists in pleasure boats cruising the Great Loop. The Illinois River is an important part of the Great Loop, the circumnavigation of Eastern North America by water.


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 glacier melted, the Illinois River flowed into the ancient channel. The Hennepin Canal roughly follows the ancient channel of the Mississippi upstream of Rock Island.

The modern channel of the Illinois River was shaped in a matter of days by the Kankakee Torrent. During the melting of the Wisconsin Glacier about 10,000 years ago, a lake formed in present-day Indiana, comparable to one of the modern Great Lakes. The lake formed behind the terminal moraine of a substage of that glacier. Melting ice to the north eventually raised the level of the lake so that it overtopped the moraine. The dam burst, and the entire volume of the lake was released in a very short time, perhaps a few days.

Because of the manner of its formation, the Illinois River runs through a deep canyon with many rock formations. It has an “underutilised channel,” one far larger than would be needed to contain any conceivable flow in modern times.

Vacation Cruises

The Illinois River offers vacation cruises unlike any other river in the world. The rich history, beautiful scenery, and abundant wildlife all make the Illinois River a true natural treasure.

The Spirit of Peoria offers overnight Illinois River cruises from May through October.

The Illinois Waterway System

The Illinois Waterway System operates with eight dams that hold back water to form pools that resemble long narrow lakes. These dams raise the water level, making the river deep enough for large rivercraft that require nine feet of water to operate. This arrangement creates a “stairway of water” which drops 163 feet from lake Michigan to the Mississippi River. Once below St. Louis, the Mississippi is naturally deep enough so there is no longer a need for dams.


Illinois River Trivia

Length 273mi (439km)
Source Confluence of the Kankakee and Des Plaines Rivers, elevation 505ft (154m)
Mouth Mississippi River, elevation 417ft (127m)
Average Discharge 23,200ft3/s (657m3/s)
Wildlife includes Eastern bluebird, Henslow sparrow, American bittern, black-crowned night heron, black and sora rails, bald eagle, river otter, muskrat, beaver, mink, bog lemming, prairie king and western ribbon snakes, plains leopard, and northern cricket frogs.
Other Facts Drains approximately 30,000 square miles of land and its drainage extends slightly into Wisconsin and Indiana.
Forms the greater part of the Illinois Waterway, which links the Great Lakes with the Mississippi.
Chief city on the river is Peoria.
Scientists have studied the geology and biology of the Illinois River for over 100 years—leading some to call it the “most studied river in the world.”