Mahoning

River flowing through Ohio and Pennsylvania, USA; length 140 km/90 mi. It rises in Columbiana County, eastern Ohio, and joins the Shenango River to form the Beaver River.

Course From its source it flows northwest to Alliance, then northeast by way of dam-created Berlin Lake and Lake Milton, to Newton Falls and Warren. It then turns southeast and flows through the area known as the Mahoning Valley, past Youngstown, and into northwestern Pennsylvania, to New Castle, where it joins the Shenango.

The Mahoning Valley was an early focus of the steel industry, since regional coal and Great Lakes iron ore could be easily delivered to its plants; but by the later 19th century railway transportation had reduced the area's advantage, and the valley entered into a long, gradual decline.