Watertown is a city in Dodge and Jefferson Counties in the U.S. state of Wisconsin. Most of the city's population is in Jefferson County. Division Street, several blocks north of downtown, marks the county line. The population of Watertown was 21,598 at the 2000 census. Its 2007 estimated population was 23,301. Watertown is the largest city in the Watertown-Fort Atkinson micropolitan area, which also includes Johnson Creek and Jefferson. The 2005 estimated population of the micropolitan area was 79,328.