Puget Sound Regional CouncilPSRC utilizes assessor data extracts for King, Kitsap, Pierce, and Snohomish counties to estimate housing development at the parcel level for each year in this time series. The methodology utilizes variables that identify Residential Uses, Number of Units, and Number of Buildings together with a Year Built variable to estimate new housing units built annually by structure type. The most current vintage of residential assessor records are then related back to a base year record set to determine what type of development took place on a given parcel. Development activity types tracked are: 'New Development', 'Redevelopment', and 'Rebuild/Remodels'. For Redevelopment and Rebuild/Remodels, base year unit counts are categorized as 'Demolitions' and subtracted from the inventory to calculate net change. The annual net housing unit estimates are summarized by county, jurisdiction, and census tract. The starting year in the time series will vary by county due to base year datasets differing from county to county. The time series for each county is as follows: King County: 2010-2024 Kitsap County: 2010-2024 Pierce County: 2012-2024 Snohomish County: 2011-2024 A new time series will be processed and published each year. Please note the estimates may shift from version to version due to updates in the data inputs and methodology refinements. Group Quarter Facilities are omitted from the final estimates. Unit counts for Mobile Home Parks are held constant except when an existing park is closed or redeveloped or a new park is opened. The 'Single-Family Attached' structure type category is defined in each county by the following: King: 'Townhouse Plat' present use category in the parcel table Kitsap: House type code '146 Townhouse' in the dwellings table Pierce: Built-As IDs 61, 65, and 68 in the improvements built-as table Snohomish: Property Class Codes 116 and 142 in the master table Missing Unit/Building Counts Housing unit and building counts are not available in the Snohomish County assessor datasets. Unit counts for single family parcels were assumed to = 1. Unit counts for multi-family parcels were populated by using utility hookup counts from the Snohomish County Public Utilities District (PUD). Building counts were populated by using a mix of utility customer property data and structure type information. Kitsap: Unit counts are accessed through a supplemental data request to the Kitsap County Department of Community DevelopmentArcGIS FeatureLayerhttps://hub.arcgis.com/datasets/f90becabc0664515942f3921caff68ba_0engPuget Sound Regional Council Data PortalPublicAnnual Housing Development Estimates by County [Washington (State)--Puget Sound Region]Web servicesWashington (State)--Puget Sound RegionWashington (State)Last Modified: 2026-01-09