The Superior Court of Washington for King County is the largest trial court in Washington state. It is based at the King County Courthouse, 516 Third Avenue, in downtown Seattle, Washington. It also operates a juvenile facility and a Regional Justice Center in Kent, southeast of Seattle.

King County is located in the U.S. state of Washington. The population was 2,269,675 in the 2020 census, making it the most populous county in Washington, and the 12th-most populous in the United States. The county seat is Seattle, also the state's most populous city.