The original Elmsley Township, which included both South Elmsley and North Elmsley, was surveyed in 1803-1804. It was named after John Elmsley, Chief Justice of Upper Canada from 1796 to 1802 and Chief Justice of Lower Canada from 1802 until his death in 1805. South Elmsley containing concessions one to five was incorporated as a separate township in 1851 and included in Leeds County. North Elmsley which contains concessions five to ten, is part of Lanark County. The Rideau River and Rideau Lake form the boundary between the two Elmsleys.