State Route 104 (SR 104) is a 31.75-mile-long (51.10 km) state highway in the U.S. state of Washington, serving four counties: Jefferson on the Olympic Peninsula, Kitsap on the Kitsap Peninsula, and Snohomish and King in the Puget Sound region. It begins south of Discovery Bay at U.S. Route 101 (US 101) and crosses the Hood Canal Bridge over Hood Canal to the terminus of SR 3 near Port Gamble. SR 104 continues southeast onto the Edmonds–Kingston Ferry to cross the Puget Sound and intersects SR 99 and Interstate 5 (I-5) before ending at SR 522 in Lake Forest Park. SR 104 also has a short spur route that connects the highway to SR 99 at an at-grade signal on the Snohomish–King county line.

Jefferson County is a county located in the U.S. state of Washington. As of the 2020 census, the population was 32,977. The county seat and only incorporated city is Port Townsend. The county is named for Thomas Jefferson.