King's Highway 51, commonly referred to as Highway 51, was a provincially maintained highway in the Canadian province of Ontario that connected Highway 3 in Eatonville with Rondeau Provincial Park. An earlier designation existed south of Orangeville, connecting Highway 24 with Highway 10. This iteration was assumed in 1938, but later renumbered as Highway 24 In 1961. The more recent incarnation of the route number was assumed in 1970, but then decommissioned in 1997 and transferred to what is now the city of Chatham–Kent.