San Juan County, Washington

San Juan County
San Juan County Courthouse
Motto: 
A World Away
Location within the U.S. state of Washington
Washington's location within the U.S.
Coordinates: 48°34′N 122°58′W / 48.57°N 122.97°W / 48.57; -122.97
Country United States
State Washington
FoundedOctober 31, 1873
Named afterSan Juan Islands
SeatFriday Harbor
Largest townFriday Harbor
Area
  Total
621 sq mi (1,610 km2)
  Land174 sq mi (450 km2)
  Water447 sq mi (1,160 km2)  72%
Population
 (2020)
  Total
17,788
  Estimate 
(2024)
18,668
  Density96/sq mi (37/km2)
Time zoneUTC−8 (Pacific)
  Summer (DST)UTC−7 (PDT)
Congressional district2nd
Websitewww.sanjuanco.com

San Juan County is a county in the Salish Sea in the far northwestern corner of the U.S. state of Washington. As of the 2020 census, its population was 17,788. The county seat and only incorporated town is Friday Harbor, on San Juan Island. The county was formed on October 31, 1873, from Whatcom County and is named for the San Juan Islands, which are in turn named for Juan Vicente de Güemes, 2nd Count of Revillagigedo, the Viceroy of New Spain.

Although the islands have no state highways, the ferry routes serving them are designated as part of the state highway system.