Thornhill is a federal electoral district in Ontario, Canada, that has been represented in the House of Commons of Canada since 1997. It covers the community of Thornhill, which is made up of portions of Vaughan and Markham, and was created in 1996 from parts of Markham—Whitchurch—Stouffville and York North ridings. 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.