Perth is a town in Eastern Ontario, Canada. It is located on the Tay River, 83 kilometres (52 mi) southwest of Ottawa, and is the seat of Lanark County.

Eastern Ontario is a secondary region of Southern Ontario in the Canadian province of Ontario which lies in a wedge-shaped area between the Ottawa River and St. Lawrence River. It shares water boundaries with Quebec to the north and New York State to the east and south, as well as a small land boundary with the Vaudreuil-Soulanges region of Quebec to the east.