Sumner is a town in Jefferson County, Wisconsin, United States.

[3] The census-designated place of Lake Koshkonong and the unincorporated communities of Busseyville, Carcajou, Glenn Oaks Beach, Koshkonong Manor, and North Shore are located within the town.

As of the census[2] of 2000, there were 904 people, 370 households, and 259 families residing in the town.

The racial makeup of the town was 98.89% White, 0.33% Native American, 0.22% Asian, 0.11% Pacific Islander, and 0.44% from two or more races.

23.2% of all households were made up of individuals, and 13.5% had someone living alone who was 65 years of age or older.