 State Route 221 ( SR 221 ) is a 25 @.@ 95 @-@ mile ( 41 @.@ 76 km ) long state highway located entirely within 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 and was designated as Primary State Highway 8E from 1937 until the 1964 renumbering of Washington state highways . 
