Ohio River
none of the rivers form the southern border of Indiana, but the Ohio river forms the southern border of Ohio.
The Wabash River forms the easter border of Illinois. I've noticed that the previous answer was the Ohio River. The Ohio River actually is what runs along the southern tip of Illinois.
The Wabash River forms the southern portion of Indiana's western border. The northern portion of Indiana's western border is simply a straight line marked on the map. The southern border of Indiana is also a river - the Ohio.
West Virginia, Ohio, Illinois, and Indiana form the northern border of Kentucky, along the Ohio River.
The Ohio River forms the borders of West Virginia, Ohio, Kentucky, Indiana, and Illinois. The border terminates at the confluence with the Mississippi and the border with Pennsylvania.
Ohio River
The Ohio River forms Ohio's southern border.
The Ohio River
The Ohio River and Lake Erie. the Mississippi river goes through Ohio
Ohio river, beckley river, fayyette river, and elk river
The Rio Grande forms part of the border between the US and Mexico.