Wellington—Dufferin—Simcoe was a federal electoral district represented in the Canadian House of Commons from 1979 to 1988. It was located in the province of Ontario. This riding was created in 1976 as Dufferin—Wellington and renamed in 1977. It was created from parts of Halton, Peel—Dufferin—Simcoe and Wellington—Grey—Dufferin—Waterloo ridings.
It consisted of the County of Dufferin, the Townships of Adjala and Tosorontio and the Town of Alliston in the County of Simcoe, and Townships of Arthur, Erin, Maryborough, Minto, Nichol, Peel, West Garafraxa and West Luther, including the Towns of Mount Forest and Palmerston in the County of Wellington.
The electoral district was abolished in 1987 when it was redistributed between Guelph—Wellington, Perth—Wellington—Waterloo, Simcoe Centre, Wellington—Grey—Dufferin—Simcoe and York—Simcoe ridings.