Benton County is located in south-central Washington. The county seat is located in Prosser, and its largest city is Kennewick. Benton County was created on March 8, 1905 and was named after U.S. Senator Thomas Hart Benton. Benton County operates under the plural executive form of government with three commissioners and seven other elected officials. Benton County has offices located in Prosser and Kennewick. For more information, please visit our website.