Benton County is a county located in the south-central portion of the U.S. state of Washington. The Columbia River makes up the north, south, and east boundaries of the county. As of the 2010 census, its population was 175,177. The county seat is Prosser, and its largest city is Kennewick. It was named after Missouri Senator Thomas Hart Benton.
Benton County was created out of Klickitat County and Yakima County on March 8, 1905.