State Route 9 (SR 9) is a 98.17-mile (157.99 km) long state highway traversing three counties, Snohomish, Skagit and Whatcom, in the U.S. state of Washington. The highway extends north from an interchange with SR 522 in the vicinity of Woodinville north through Snohomish, Lake Stevens, Arlington, Sedro-Woolley and Nooksack to become British Columbia Highway 11 (BC 11) at the Canadian border in Sumas.