Cashel, Ontario is a small hamlet situated in Unionville, Ontario located at the intersection of Elgin Mills Road and York Regional Road 67. Originally it was called Crosby Corners after John Crosby (born 1797), the village's first store owner, who came originally from New York State. The name was changed to Cashel in 1851 with the opening of its first post office. It was likely named after Cashel in Ireland. In 1851 the community had a sawmill, cobbler shop, blacksmith shop, wagon shop, inn and tavern, Masonic Lodge, and Presbyterian church.