largest southward-flowing tributary of the Ohio River, rising in Grand Lake, western Ohio. It flows generally westward across Indiana past the cities of Huntington, Wabash, Logansport, and Lafayette, then southward to Terre Haute. Just south of that city it forms a 200-mile (320-kilometre) boundary between Indiana and Illinois and then enters the Ohio in the southwestern corner of Indiana after a total course of 529 miles (851 km). The Wabash drains an area of about 33,150 square miles (85,860 square km). Its chief tributaries are the White (White River) and Tippecanoe (Tippecanoe River) rivers, both entering from the north. Other tributaries, all flowing from the north, are the Little Wabash, Embarrass, and Vermilion. At Mount Carmel, Ill. (75 miles 【120 km】 above the mouth of the river), the average flow is 30,400 cubic feet (860 cubic m) per second.

During the 18th century the French used the Wabash as a transportation link between Louisiana and Quebec. After the War of 1812, the Wabash basin was rapidly developed by settlers, and the river continued as an important artery of trade, for both flatboats and river steamers. River navigation, apart from barge traffic on its lower course, almost completely disappeared after the coming of the railroads in the 1850s.

The name Wabash is derived from a Miami Indian word meaning “shining white” or “water over white stones.”