How Realigned Ancient Rivers Influenced the Illinois Border Locations.

The borders of Illinois were established when Illinois became a state in 1818. The western border was delineated using the Mississippi River, and the Ohio River was used as the southern border. The eastern border was formed by the Ohio and Wabash rivers as well as the line along the current longitude line of 87°31', connecting the Wabash River to Lake Michigan. As initially proposed, the northern border of Illinois would have been 51 miles to the south of the current latitude line of 42°30'30". This 5,440,000-acre addition to Illinois assured that the territory met the required minimum of 40,000 people to qualify as a state. [ABSTRACT FROM AUTHOR]