Waterloo is a town in Jefferson County in the U.S. state of Wisconsin.

The unincorporated community of Portland is also located partially in the town.

According to the United States Census Bureau, the town has a total area of 32.3 square miles (83.7 km2), all land.

There were 312 housing units at an average density of 9.7 per square mile (3.7/km2).

13.7% of all households were made up of individuals, and 6.4% had someone living alone who was 65 years of age or older.