Highway 51 was a short connector road that served to link Highway 3 to Rondeau Provincial Park. At its southern terminus, the highway began at the entrance gates to the provincial park, proceeding northeast through a small community of recreational cottages. The highway exited the park and turned north onto what is now Chatham–Kent Road 15. From here the highway progressed straight north to Highway 3, passing through the community of New Scotland along the way. Trees continue to line both sides of this section of the highway, with farmland sprawling out beyond that.
In 1961, the section of Highway 24 between Highway 51 and Orangeville was renumbered as Highway 136; Highway 51 was renumbered as Highway 24 and the latter signed concurrently with Highway 10 north to Orangeville. On April 9, 1970, the road from Eatonville to Rondeau Provincial Park was designated as Highway 51. This iteration of the route remained unaltered until April 1, 1997, when it was transferred to Kent County, now the City of Chatham–Kent. It was subsequently designated as Chatham–Kent Road 15.