High Quality Content by WIKIPEDIA articles! State Route 221 (SR 221) is a 25.95-mile (41.76 km) long state highway located entirely with in Benton County, Washington, United States. The highway serves to connect the unincorporated community of Paterson to the county seat Prosser. The highway has existed since at least 1926 as Primary State Highway 8E until the 1964 renumbering of Washington state highways.