Watertown is a city in, and the county seat of, Jefferson County, New York, United States. It is approximately 25 miles (40 km) south of the Thousand Islands, along the Black River about 5 miles (8 km) east of where it flows into Lake Ontario. The city is bordered by the town of Watertown to the south, east, and west, and is served by the Watertown International Airport and the Watertown Daily Times newspaper. In the middle of Watertown lies the Public Square Historic District, which was built in 1805 and listed on the National Register of Historic Places (NRHP) in 1984. Watertown is located 13 miles (21 kilometers) southwest of the U.S. Army base at Fort Drum; it is the service and shopping destination for personnel there and their families. As of the 2020 United States Census, the city has 24,685 residents, making it the largest city in the North Country.