State Route 203 (SR 203) is a state highway in the U.S. state of Washington that traverses part of King and Snohomish counties. It runs north–south through the Snoqualmie Valley, connecting Fall City, Carnation, Duvall, and Monroe. The highway terminates to the south at a roundabout with SR 202 near Fall City and to the north at a junction with U.S. Route 2 (US 2) in Monroe. The road network along the Snoqualmie River developed in the early 20th century to connect communities that had been established near a branch of the Chicago, Milwaukee, St. Paul and Pacific Railroad. These county roads were paved and added to the state highway system in 1937 as Secondary State Highway 15B (SSH 15B), which served as a connector between state highways in Fall City and Monroe. SSH 15B was straightened and rebuilt by the state government in the 1940s and 1950s before being replaced by SR 203 during the 1964 state highway renumbering. SR 203 was included as part of the proposed corridor for an outer freeway bypass, tentatively named Interstate 605, in the early 2000s. The highway was later improved by a series of construction projects, including the construction of two roundabouts in Fall City and Duvall. Route description SR 203 begins at a roundabout with SR 202 on the north side of the Snoqualmie River opposite from downtown Fall City. The highway travels northwest along the river, following the eastern ridge of the rural Snoqualmie Valley and the Snoqualmie Valley Trail, and turns north near Pleasant Hill. After passing several farms and a golf course, SR 203 crosses over the Tolt River and enters the city of Carnation. The highway runs northeasterly through downtown Carnation on Tolt Avenue, passing the city library and the historic Tolt IOOF/Eagles Hall before leaving the city. After crossing the Snoqualmie Valley Trail at the Chinook Bend north of Carnation, SR 203 reaches Lake Marcel and turns northwest to follow the Snoqualmie River around Novelty Hill. The highway then turns north and intersects Northeast 124th Street in a roundabout before entering Duvall, where it passes through downtown on Main Street. SR 203 continues northeast across the Cherry Valley and turns northwest before it reaches the Snohomish County line. The highway traverses the Tualco Valley and passes several farms, including one operated by the Monroe Correctional Complex, before crossing over the Skykomish River on a steel truss