Sumner is a city in Bremer County, Iowa, United States. The city is located along the county's eastern border, between Bremer and Fayette counties. The population was 2,030 at the time of the 2020 census. The Bremer County portion of Sumner is part of the Waterloo–Cedar Falls Metropolitan Statistical Area. The town was established in 1870, and incorporated in 1894. The community is named after American political leader Charles Sumner.