Waterloo is a city in Jefferson County in the U.S. state of Wisconsin. As of the census of 2010, the population was 3,333.
Waterloo is located at 43°11′1″N 88°59′23″W, (43.18366, -88.989965) at the intersection of Wisconsin Highway 89 and Wisconsin Highway 19 in northwestern Jefferson County.
According to the United States Census Bureau, the city has a total area of 3.91 square miles (10.13 km2), of which, 3.83 square miles (9.92 km2) is land and 0.08 square miles (0.21 km2) is water.
As of 2000 the median income for a household in the city was $50,221, and the median income for a family was $56,446. The per capita income for the city was $23,011. About 5.0% of families and 4.8% of the population were below the poverty line, including 5.8% of those under age 18 and 7.1% of those age 65 or over.
As of the census of 2010, there were 3,333 people, 1,331 households, and 867 families residing in the city. The population density was 854.6 people per square mile (330/km2). There were 1,409 housing units at an average density of 361.3 per square mile (139.5/km2). The racial makeup of the city was 89.20% White, 0.80% Black or African American, 0.40% Native American, 0.80% Asian, 9.40% from other races, and 1.20% from two or more races.