Provisional and Territorial Records Guide
King County History and Records
King County was formed by the territorial legislative assembly on December 22, 1852 from the northern part of Thurston County. The county was named for the thirteenth vice president of the United States, William King. King County's original borders were Jefferson County and Puget Sound on the north, the Pacific Ocean on the west, Thurston and Pierce Counties on the south, and the Cascades on the east.
On January 6, 1853, an act passed by the legislative assembly located the county seat at Seattle, on the land claim of David Maynard. Another act, passed the same day, appointed county officers, including three commissioners, a sheriff, and a probate clerk. At first, judicial jurisdiction was to be shared with Pierce County, but an act of January 21, 1853, ordered King County to establish its own US district court. The judge assigned to Pierce and Island Counties was to appoint a clerk for the King County US District Court.
Other laws involving King County during this period included the order for the equitable distribution of school funds from Thurston County to King County and the authorization of the county commissioners to levy a road tax. On March 2, 1853, Washington Territory was created and King County was removed from the jurisdiction of the Oregon Territory.