Wabash River, the largest and longest river in Indiana and the largest of the Ohio River's tributaries from the north. The river is 475 miles (764 km) long. The Wabash's source is in Darke County, Ohio. The river crosses Indiana's eastern border near its center and then flows northwest to Huntington; southwest to Logansport, Lafayette, and Covington; and south to Terre Haute. After a westward jog, it then flows southward through Vincennes and New Harmony to join the Ohio River, separating Indiana from Illinois for the last 150 miles (240 km) of its course.

The Wabash became an important thoroughfare for French explorers and fur traders in the latter part of the 17th century. They called it by its Indian name (meaning "white"), which they spelled Ouabache.