The Washington State Legislature extended the roadway north to end at US 101 south of Queets through tribal lands, although this segment has yet to be built.

SR 109 was first established as Secondary State Highway 9C (SSH 9C) in 1937, which was on a more northern alignment until 1947, when it was switched to a Hoquiam to Quinault Indian Reservation route.

[3] Both directions of SR 109 continue west on Emerson Avenue through a residential area of Hoquiam, passing several schools and parks while following a short branch of the Puget Sound and Pacific Railroad.

[4] The railroad ends at the edge of Bowerman Basin, where SR 109 intersects a spur route that serves as a northern bypass of Hoquiam.

SR 109 runs inland through a forested area on the bluff and turns north to cross Grass Creek and follow the shore around the northeast side of Grays Harbor.

[7] The highway turns north to follow the Pacific Coast, passing through the residential area of Ocean City, where it swerves a block east.

[6] SR 109 continues north along the Pacific Coast, which has several public access points for beaches and state parks,[8] and passes several private resorts and campgrounds.

The highway passes through the community of Seabrook, a modern planned development near Roosevelt Beach laid out with New Urbanist principles and inspired by New England's coastal towns.

[12] SR 109 functions as the main access to the Quinault Indian Reservation and Ocean Shores as well as a major tsunami evacuation route.

[22][23] The Quinault Nation also opposed its construction due to potential disruption to their lifestyle, but later relented and signed a memorandum of understanding with the state government in October 1984.