History of King's Highway 51 (#1):
The first King's Highway 51 was a minor local highway in Peel County which served as a connecting route between Highway 24 and Highway 10 near Caledon. Highway 51 was first established in the late 1930s. In September 1937, a Preliminary Route Plan was prepared for two proposed King's Highways in Peel County. The first route, which was designated as an extension of Highway 24, ran from the Wellington-Peel County Boundary southwest of Caledon to Coulterville. Highway 24 branched off at Coulterville towards Alton and Orangeville. The second road, from Coulterville to the Highway 10 Junction in Caledon, was assumed as a new King's Highway by the Department of Highways of Ontario (DHO) on April 13, 1938. This new route was designated as King's Highway 51. The route was only 4.5 km in length, making it one of the shortest provincial highways to ever exist in Ontario. Highway 51 initially had a gravel surface but the entire route was paved in 1959. Highway 51 survived until the early 1960s, when a route renumbering in the Caledon area erased Highway 51 from the map. In 1961, Highway 24 was rerouted between Coulterville and Orangeville. The original route of Highway 24 between Coulterville and Orangeville via Alton was renumbered as Highway 136. As a result of this route renumbering, Highway 10 & Highway 24 were signed concurrently between Orangeville and Caledon, while the route of Highway 51 from Coulterville to Caledon was absorbed in its entirety into the relocated route of Highway 24. A different, unrelated Highway 51 existed near Chatham between 1970 and 1997.