Sullivan is a village in Jefferson County, Wisconsin, United States. The population was 651 at the 2020 census. The village is located within the Town of Sullivan, and is known to residents of southern Wisconsin including the Madison and Milwaukee metro areas as the location of the National Weather Service forecast office MKX, although its mailing address is in nearby Dousman.

Jefferson County is a county in the U.S. state of Wisconsin. As of the 2020 census, the population was 84,900. Its county seat is Jefferson. Jefferson County comprises the Watertown-Fort Atkinson, WI Micropolitan Statistical Area, which is also included in the Milwaukee-Racine-Waukesha, WI Combined Statistical Area.