Watertown is a city in the U.S. state of New York and the county seat of Jefferson County. It is situated approximately south of the Thousand Islands, and along the Black River about east of its mouth at Lake Ontario. It lies northwest of Albany, the state capital, and northwest of New York City. As of the 2010 census, it had a population of 27,023, an increase of 1.2% since 2000. The U.S. Army post Fort Drum is near the city.