World Facts

The 10 Longest Rivers in Illinois

The longest river entirely situated within the state of Illinois is the Kaskaskia River.

Illinois has roughly 880 miles of rivers bordering it and more than 87,000 miles of streams and rivers within its borders. These water bodies range in size and length with some of the longest rivers within the state ranking among the longest in the world. The Mississippi spans 581 miles of its length to form the western border making it the longest river in Illinois. The Illinois and Kaskaskia rivers have their entire length running within the state ranking among the 10 longest rivers in the state.

The Longest Rivers in Illinois

Mississippi River

The Mississippi River is the world’s 4th longest river and North America’s second longest river. This river drains 31 states of the US and two Canadian provinces. The Mississippi flows through 10 states and out of these, Illinois has the largest population living along the river. It generally flows in a southerly direction from it source at Lake Itasca in Northern Minnesota down to its delta at the Gulf of Mexico. The Mississippi has more than 15 tributaries joining it at different points along its entire length of 2,530 miles. This river is estimated to host at least 360 species of fish and support more than 326 bird species.

Ohio River

The Ohio River rises from the merger of the Monongahela and Allegheny rivers in Pennsylvania. It flows into Ohio, Indiana, and finally into Illinois where it meets the Mississippi at Cairo. Altogether the length of the river is 981 miles. This river flows through or the borders of six states. Its drainage basin cover most parts of 15 states in the US. The Ohio River forms the largest tributary of the Mississippi and at their confluence, the Ohio is significantly bigger.

Wabash River

The Wabash is an important tributary of the Ohio River. It is 503 miles long, flowing southwest from its source near the Indiana border in northwest Ohio. It flows to southern Illinois where it forms the border between the two states - Indiana and Illinois. One of its main tributaries is the Little Wabash River a 240-mile-long river fed by the Fox River, Elm River, and the West Branch Little Wabash River.

Kaskaskia River

The Kaskaskia River is the longest river that is entirely within the Illinois state. Kaskaskia is a 325-miles-long tributary of the Mississippi River. The river rises from central Illinois and flows in a southerly direction to meet the Mississippi near Chester which is 10 miles northwest of the river. The lower ends of the river’s course have been made into canals allowing for barge transport.

Other Rivers in Illinois

The top 10 rivers in Illinois have a length of more than 195 miles with the Embarras River ranking tenth. The Embarras is a tributary of the Wabash River and has its source in Champaign County. The Illinois River which springs from the union of the Des Plaines and Kankakee is the sixth-longest river in the state with a length of 273 miles. It drains a significantly large area of 29,000 square miles and forms the Peoria Lake along its course.

The 10 Longest Rivers in Illinois

RankRiverLength (miles)Length (km)
1Mississippi River2,3203,730
2Ohio River9811,579
3Wabash River503810
4Kaskaskia River325523
5Rock River299481
6Illinois River 273439
7Sangamon River246396
8Little Wabash River240390
9Fox River199320
10Embarras River195314

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