Lat/Long: 36.9833, -89.1333
The largest tributary of the Mississippi River, the Ohio River is also one of the most politically important rivers in the United States, marking the southern borders of Illinois, Indiana, and Ohio, as well as the northern borders of Kentucky and West Virginia. A major avenue for trade to the West and into the Mississippi, its source is located at Pittsburgh, Pennsylvania, and it passes Cincinnati, Ohio, near its midway point. The Ohio also served the important political role of marking the dividing line between slave and free states--much more so than the famous Mason-Dixon line between Maryland and Pennsylvania.
Wester's New Geographical Dictionary (Springfield, MA: Merriam-Webster, 1988), 882.