Waterloo is a city in Jefferson County in the U.S. state of Wisconsin. As of the census of 2022, the population was 3,628. The name Waterloo was suggested by Mr. Wilt, a Frenchman living here, who was one of Napoleon's soldiers, at the battle of Waterloo. Waterloo is located in the Watertown-Fort Atkinson micropolitan area which is a sub-market of the larger Milwaukee-Racine-Waukesha CSA.

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.