The United Farmers of Ontario (UFO) was an agrarian and populist provincial political party in Ontario, Canada. It was the Ontario provincial branch of the United Farmers movement of the early part of the 20th century.

The 1919 Ontario general election, held on October 20, 1919, elected 111 Members of the 15th Legislative Assembly of Ontario ("MLAs"). The United Farmers of Ontario captured the most seats but only a minority of the legislature. They joined with 11 Labour MPPs and three others to form a coalition government, ending the 14-year rule of Ontario's Conservatives. This is one of the few examples of coalition government in Canadian history.