what county is sumner, wa in?
Sponsored Topics. Sumner is a city in northern Pierce County, Washington, United States. The population was 9,451 at the 2010 census. Nearby cities include Puyallup to the west, Auburn to the north, and Enumclaw to the east. Sumner was platted in 1883 by George H. Ryan, and was named for the 19th century U.S. Senator Charles Sumner.