Cornwall is a city in eastern Ontario, Canada and the seat of the United Counties of Stormont, Dundas and Glengarry, Ontario. Cornwall is Ontario's easternmost city, located on the St. Lawrence River and Highway 401, and is the urban centre for surrounding communities, which include Long Sault and Ingleside to the west, Mohawk Territory of Akwesasne to the south, St. Andrew's and Avonmore to the north, and Glen Walter, Martintown, Williamstown, and Lancaster to the east.

Cornwall is located approximately 100 kilometres (60 mi) southeast of Ottawa, Canada's capital, 100 kilometres (60 mi) southwest of Montreal, Quebec's largest city, and 400 kilometres (250 mi) northeast of Toronto, Ontario's capital.