River - Wabash
The Wabash River, a tributary of the Ohio River, forms the southeastern border of Illinois. Its major Illinois tributaries include the Little Wabash River, Embarras River, and Vermilion River. The Wabash flows south from Indiana, meeting the Illinois border in Clark County. For roughly 200 miles, the Wabash flows along the shared border of Illinois and Indiana before draining to the Ohio River in Gallatin County.