Bridge over the Ohio River in Cairo, Illinois
Image Source: © 2011 Jonathunder on Wikimedia
The Ohio River is the Mississippi River's largest tributary, forming near Pittsburgh from the Allegheny and Monongahela Rivers and joining with the Mississippi 981 miles later in Cairo, Illinois. The Ohio River borders or flows through Illinois, Indiana, Kentucky, Ohio, Pennsylvania and West Virginia. Nearly 10% of the U.S. population, about 25 million people, live in the Ohio River Basin and more than 5 million people rely on the river for drinking water.
Source: Ohio River Foundation
This page focuses primarily on documents related to Illinois portion of the Ohio River Basin, where flows along the southern border from where the Wabash joins it in Gallatin County to it's confluence with the Mississippi River near Cairo, Illinois.