The highway, travelling north parallel to the Green River, begins at SR 516 in Kent and ends at an interchange with Interstate 405 (I-405) in Tukwila.

The original route, between Auburn and Rainier Valley in Seattle, was originally established in 1931 as a branch of Primary State Highway 1 (PSH 1) and in 1937 as Secondary State Highway 5M (SSH 5M).

[4] SR 181 begins to parallel a BNSF and Union Pacific rail line to the east as it serves Tukwila Station.

[5][6][7] The highway ends at a partial cloverleaf interchange with I-405, crossing over the Green River shortly before its northern terminus.

[8][9] The West Valley Highway was built in the early 1910s, after an alignment on the west side of the White (now Green) River Valley was chosen by county engineers in 1909.