Ohio River course forms the northern borders of West Virginia and Kentucky; and the southern borders of Ohio, Indiana and Illinois, until it joins the Mississippi River at the city of Cairo, Illinois. Where the Ohio joins the Mississippi is the lowest elevation in the state of Illinois, at . The Ohio River, which flows westward from Pittsburgh, Pennsylvania, to Cairo, Illinois, is the largest tributary, by volume, of the Mississippi River in the United States. At the confluence, the Ohio is considerably bigger than the Mississippi. Measured by long-term mean discharge in cubic feet per second and cubic meters per second,
Fox River (Illinois River tributary) near the Fox River included the Potawatomi, Sac, and Fox tribes. The Fox River has 15 dams, including McHenry Dam, which raises the river slightly to maintain depth in the Chain O'Lakes in northern Illinois, and a hydroelectric dam near Ottawa. In the winter, bald eagles can be found nesting along the banks. Early in the history of Illinois, the Fox River provided water for the Illinois and Michigan Canal via a feeder canal, allowing the canal to pass over the Fox River on an aqueduct. In 1996, a flood damaged the Farnsworth House in Illinois, a residence designed by