SR 3 begins at a diamond interchange with US 101 south of Shelton in unincorporated Mason County on the Olympic Peninsula. The highway travels north into Shelton at the end of Oakland Bay on 1st Street and crosses over a Puget Sound and Pacific Railroad line and Goldsborough Creek. SR 3 turns east on Pine Street and leaves Shelton, traveling northeast along Oakland Bay and a US Navy rail line. The highway continues north along Oakland Bay and Case Inlet past heavily forested areas to Allyn-Grapeview, where it serves as the western terminus of SR 302 at North Mason High School. SR 3 travels towards the southern end of the Hood Canal and intersects the eastern termini of SR 106 and SR 300 in Belfair. The highway continues northeast past Bremerton National Airport towards the community of Gorst in Kitsap County, where it forms the western terminus of SR 16.