Formed by the confluence of the Allegheny River, Allegheny and Monongehela Rivers at Pittsburgh, the Ohio forms part of the border between Ohio and West Virginia, between Ohio and Kentucky, between Ohio and Indiana, and between Illinois and Kentucky before joining the Mississippi at Cairo, Illinois.
Since it was considered by pre-Columbian inhabitants of eastern North America to be part of a single river continuing on through the lower Mississippi, it is perhaps an understatement to characterize the Ohio as a mere tributary of the Mississippi.
Besides Pittsburgh, other cities along the Ohio include:
- Wheeling, Marietta, Steubenville, Portsmouth and Cincinnati in Ohio
- Parkersburg in West Virginia
- Louisville and Henderson in Kentucky
- Madison, Albany, Tell City, Evansville and Mount Vernon in Indiana.