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
New York State Route 51 north from West Winfield to Utica. At the time, this was the only substantial segment of what is now NY 51 to have a route number even though all of modern NY 51 south of Ilion was state-maintained. In the 1930 renumbering of state highways in New York, most of NY 44 became part of NY 8. The section from West Burlington to West Winfield, however, became part of the new NY 51, which utilized all of its modern routing from Mount Upton to Ilion upon assignment. It was extended across the Mohawk River to NY 5 in North Ilion