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,
Vermilion River (Illinois River) these as a single river that flowed in two directions. It is also possible that, in early settlement times, these rivers formed a canoe route between the Illinois River and Wabash River, with a portage through the marshes near Roberts. This may explain why the two rivers have the same name. The north-flowing Vermilion flows in a northerly direction from its origin in Livingston and Ford counties in north central Illinois, eventually emptying into the Illinois River, near Oglesby. Perhaps it is best known for its stretch of whitewater between Lowell and Oglesby, Illinois, which is one of few found