From the website:
The Northwest Regional Branch provides archival and records management services to local government agencies throughout Clallam, Island, Jefferson, San Juan, Skagit, Snohomish, and Whatcom counties.
The Collections at the Northwest Region
Local government records include those from county offices such as the Auditor, the Clerk, the Treasurer, the Board of Commissioners, and from municipalities, school districts, and other service districts. Only a small percentage of the records created by these offices are transferred to the State Archives as archival records. They are selected as archival for their value as legal and historical evidence of policy development, implementation, and effect. The transfer of records to the State Archives is an ongoing process. Some historical records remain with their originating office pending future transfer to the Archives.
Although the Archives does not hold all the records for the entire span of Washington's history from the various county and city offices in the region, it does hold extensive series of some records from all seven counties, with more complete representation in Whatcom, Skagit, and Snohomish counties. These series include: