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 2,021 at the time of the 2020 census. The Bremer County portion of Sumner is part of the Waterloo–Cedar Falls Metropolitan Statistical Area.

Bremer County is a county in the northeastern part of the U.S. state of Iowa. As of the 2020 Census, the population was 24,988. Its county seat is Waverly. The county was named for Fredrika Bremer, a Swedish feminist writer.