Thornhill is a federal electoral district in Ontario, Canada, that has been represented in the House of Commons of Canada since 1997. It consists of the part of the city of Vaughan that is east of Highway 400 and south of Rutherford Road, and the part of the city of Markham west of Bayview Avenue. It covers the Thornhill neighbourhood, which is split between Vaughan and Markham. The riding was created in 1996 and the east end of the riding was split off into other ridings in 2012.