Brockville, formerly Elizabethtown, is a city in Eastern Ontario, Canada, in the Thousand Islands region. Although it is the seat of the United Counties of Leeds and Grenville, it is politically independent of the county. It is included with Leeds and Grenville for census purposes only. Known as the "City of the 1000 Islands", Brockville is located on the north shore of the Saint Lawrence River, about halfway between Kingston to the west and Cornwall to the east.