The Ohio Valley usually refers to the Ohio River Valley or that area that surrounds the legendary river. Some people will use the shorthand of the Ohio Valley to refer specifically to the upper part of the Ohio River Valley rather than the entire course of the River. The largest tributary of the Mississippi River, the Ohio River winds through six states and is 981 miles long. It begins in Pennsylvania and forms borders along Ohio, West Virginia, Indiana, Kentucky, and Illinois.
A detailed Ohio valley map will include major cities like Pittsburgh (PA), Huntington (WV), Cincinnati (OH), Louisville (KY), Evansville (IN), and Paducah (KY) as well as other cities and town in the areas surrounding the river.
The Ohio River formed as a result of flooding of a glacial lake in earlier ages. It connected two now defunct rivers, the Steubenville River and the Amarietta River. This enlarged the previously small Marietta Valley. Over the course of several Ice Ages, the Ohio River drained glacial lakes and was filled with flood waters from melting glaciers until it reached modern era dimensions.
The Ohio is fed mainly by the Allegheny River with its source in Allegheny Township in Pennsylvania. A secondary source is the Monogahlea River at Fairmont, West Virginia. The mouth of the Ohio River, where it feeds into the Mississippi, is located where Cairo, Illinois meets Ballard County, Kentucky. Along the way, it has nearly a dozen tributaries that feed into the river. These include the Kentucky River, the Tennessee River, Cumberland River, Great Miami River, Kanawha River, and Big Sandy River.
On average, the Ohio River discharges 281,000 cubic feet per second. During times of high run off and floods it can reach over 1.8 million cubic feet per second.
The Ohio Valley played an important role throughout history. From pre-Columbian settlers through French explorers and traders and British rule until modern American cities, people have counted on the fertile land surrounding the river to survive. The strategic military importance of the River was also valued at various times throughout history. During the Civil War it served as the border between slave and free states.