Illinois is bordered by 880 miles of rivers and has 87,110 miles of rivers and streams within its borders. The Mississippi River, Ohio River and Wabash River are the bordering rivers of the state. The Mississippi River forms the western border of Illinois in a 581 mile stretch of its course and, as such, is the longest river in the state.
The Ice Age had major impacts on Illinois and its rivers. Glaciers blocked and buried some rivers and created new ones. Some ancient rivers, such as the Teays, Cumberland, Paw Paw and Ticona, no longer exist. The Missouri River once flowed in much of what is now the Mississippi River bed but was blocked and filled during the Kansas glacier and diverted to a new channel. The Teays River was diverted south of the glacier and became the Ohio River.
The Ohio River was important to the settlement of Illinois. In 1818 when Illinois became a state, nearly all the population was in southern Illinois, and much of it had traveled on the Ohio River. Shawneetown was the first permanent community and chief river port in eastern Illinois, being settled once in 1806 and again in 1809. Due to the salt springs 12 miles inland, in 1809 Shawneetown had more business activity than any other city in the United States west of Pittsburgh.
More than 2,900 lakes, 84,000 ponds and three large reservoirs are found in Illinois. Lake Michigan is the third largest of all the Great Lakes in area, the second largest by volume, and it is the largest body of fresh water entirely within the boundaries of the United States. Furthermore, the Lake Michigan coastline of Illinois is 63 miles long, which is a fraction of the 1,640 miles that make up the total Lake Michigan shoreline. However, despite its small size, the Illinois portion of the Lake Michigan watershed is home to half of the total population of Illinois and the lake itself is the largest public drinking water supply in the state, serving nearly 6.6 million people. This is in addition to being Illinois’ largest recreational resource and one of its biggest economic assets.
