The Wabash River is a 475 mi (765 km) long river in the eastern United States that flows southwest from northwest Ohio near St. Henry, Ohio across northern Indiana to Illinois where it forms the southern Illinois-Indiana border before draining into the Ohio River, of which it is the largest northern tributary.

When the Wisconsin Glacier melted 14,000 years ago, part of the meltwaters formed the proglacial Lake Maumee, the ancestor to Lake Erie. Eventually the meltwaters overtopped a glacial moraine located near Fort Wayne, Indiana, and catastrophically drained southwestward in the Maumee Torrent. The torrent carved the wide alluvial valley that the Wabash uses today.