Idaho State Highway 51 February 2015, some map products such as Google Maps still show SH-51's former overlay with American Legion Blvd. SH-51's northern terminus is in the city of Mountain Home in Elmore County. After turning south from Airbase Rd. and the intersection with SH-67, the road crosses the Snake River into Owyhee County and passes through the towns of Bruneau, Grasmere, and Riddle. About from the state border it enters the Duck Valley Indian Reservation. As the road crosses into Nevada it becomes State Route 225. The reservation's only major town, Owyhee is about south of the state border. After another through
Ohio State Route 51 and US 223 end here as well. The original route of State Route 51 was that of current State Route 49 in western Ohio. The route was generally changed from 51 to 49 until the entire route became 49 in 1935. A new State Route 51 was certified in 1955, with its southern terminus where it is now and its northern terminus at then-State Route 120 (close to where I-280 is now) in Northwood. State Route 51 was extended to State Route 2 in Oregon in 1959. In 1989, State Route 51 replaced the route of U.S. Route 223 though