Most plat maps have been recorded by the King County Auditor (1853-1969) and the King County Recorder's Office (1969-present). Unofficial images of all recorded plat maps are indexed and available on the King County Recorder's Office website
Original copies of most recorded plats are available for reseach at the King County Archives.
The Map Vault Collection of the King County Road Services Division can often provide researchers with electronic versions of many plat maps and recorded binding site plans.
Plats are accepted, established and modified by the King County Council (prior to 1969, the King County Commissioners). To find the actual Council ordinance or Commissioner resolution establishing or modifying a specific plat, see the county's Legislative Files or contact the King County Archives.
Additional information about the establishment or modification of plats, pre-1969, can be found in the Commissioners' plat application files (1916-1970). These applications were submitted for the final approval of a plat by the Commissioners. Individual files typically contain a certificate prepared by an attorney indicating that the ownership of the property and the payment of taxes have been verified, along with the recommendations from the office of the County Engineer. A small number of the files contain plat maps. The files are arranged by an office filing number. Contact the King County Archives for additional information and assistance.
Plats, and platted road and street rights-of-way, are vacated by the King County Council. To find the actual Council ordinance see the county's Legislative Files or contact the King County Archives.
Plat vacations prior to 1969 were sometimes made by resolutions of the King County Commissioners. More often they were made by direct orders of the Commissioners. Texts of plat vacation orders can be found in the Commissioners' Proceedings or in their plat vacation files. These files are arranged by vacation order number (5024 to 8464). They also include supporting documentation such as petitions, maps, engineers' reports and correspondence. For assistance in locating a plat vacation order, please contact the King County Archives. It is helpful if you have a date, or an approximate date, of the plat vacation.
Please read our quick tip
on locating short plats.
Sometimes old documents and maps will refer to an "unrecorded plat." Prior to 1948, some King County plats were unrecorded. Commissioners' Resolution 11048 (March 23, 1948) changed all existing unrecorded plats to "preliminary plats." Preliminary plats were generally finalized after an accurate survey was undertaken and approved. For assistance in associating a former "unrecorded plat" with a past or current tax parcel, please contact the King County Department of Assessments