The Mississippi River forms the wavy western border of Illinois. And the Ohio Wabash River is the southern border of Illinois.
The Mississippi River forms the western border of Illinois.
The river that forms the western border of Illinois is the Mississippi River.
The Mississippi River forms the western border of Illinois.
The Mississippi River.
Illinois is bordered by the Mississippi River.
Illinois is bordered by the Mississippi River on the west
the Mississippi River
Mississippi River
The Mississippi River forms the border between Missouri and Illinois.
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.
Ohio River