Washington State Route 21

State Route 21
SR 21 highlighted in red
Route information
Maintained by WSDOT
Length	191.34 mi[1] (307.93 km)
Existed	1964[2]–present
Major junctions
South end	SR 260 in Kahlotus
Major intersections	US 395 in Lind I-90 near Lind US 2 in Wilbur
North end	Highway 41 at Canadian border in Danville
Location
Country	United States
State	Washington
Counties	Franklin, Adams, Lincoln, Ferry
Highway system
State highways in Washington Interstate US State Scenic Pre-1964 1964 renumbering Former
← SR 20 → SR 22

State Route 21 (SR 21) is a 191.34-mile-long (307.93 km) state highway in the U.S. state of Washington that traverses four counties: Franklin, Adams, Lincoln and Ferry. The highway extends from an intersection with SR 260 in Kahlotus north through Lind, Odessa, Clark, Keller, Republic and Curlew before becoming Highway 41 (BC 41) at the Canadian border in Danville. SR 21 is concurrent with U.S. Route 2 (US 2) in Wilbur and SR 20 in Republic and has two diamond interchanges at US 395 in Lind and Interstate 90 (I-90) south of Odessa. Between Lincoln and Ferry counties, the roadway crosses Franklin D. Roosevelt Lake on the Keller Ferry, operated fare free by the Washington State Department of Transportation (WSDOT) and the Department of Highways (DoH) since 1930.

Since 1899, at least one segment of the current highway has been in the state highway system. In 1899, the Marble Mount Road was established and later numbered State Road 4 in 1905 and renamed to the Sans Poil-Loomis Road in 1907. In 1915, a branch to the Canadian border was added to the highway, but was removed in 1923. In 1937, the Primary state highways were established and State Road 4 became Primary State Highway 4 (PSH 4), while the former Canadian branch became Secondary State Highway 4A (SSH 4A). Another highway, extending from Lind to Wilbur, became SSH 4B. In 1964, PSH 4 was split into SR 20 and SR 21 while SSH 2A and SSH 2B also became SR 21. In 1983, a road between Lind and Kahlotus became part of SR 21.

The Keller Ferry, which travels across the Columbia River at Franklin D. Roosevelt Lake to connect the two segments of SR 21, was originally a private cable ferry operated in the early 1890s. In 1929, the Ferry and Lincoln counties unveiled a new eight-car cable ferry, named the Keller of Seattle, which served the two counties until 1930. The state highway department took over operations of the ferry in 1930 and replaced the vessel with various boats until a permanent ferry, the Martha S., was launched in 1948. The Martha S. would go on to serve until 2013, when it was retired and replaced with the more modern MV Sanpoil.