Cornwall is a city in Eastern Ontario, Canada, situated where the provinces of Ontario and Quebec and the state of New York converge. It is the seat of the United Counties of Stormont, Dundas, and Glengarry and is Ontario's easternmost city.

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.