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 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.

Jefferson County is a county on the northern border of the U.S. state of New York. As of the 2020 census, the population was 116,721. Its county seat is Watertown. The county is named after Thomas Jefferson, third President of the United States of America. It is adjacent to Lake Ontario, southeast from the Canada–US border of Ontario. The county is part of the North Country region of the state.