The Kent-Kangley Road was built as a wagon road by King County by the late 1890s and was upgraded to a paved highway after being codified as two highways during the creation of the primary and secondary state highways system in 1937: SSH 1K and SSH 5A. SSH 1K traveled 12 miles south from U.S. Route 99 and Primary State Highway 1 (PSH 1) through Burien and east through Des Moines to US 99 and PSH 1 in Midway.