This data biography includes information about who created this data, and how, where, when, and why it was collected. We (the Assessment, Policy Development, and Evaluation Unit at Public Health – Seattle & King County) created it to help you understand where the data comes from and its strengths and limitations. If you have any further questions, please don’t hesitate to reach out to us at data.request@kingcounty.gov!  

Who creates the data? 

The Washington Office of Financial Management (OFM) creates the state’s official population and housing estimates.  

Who owns the data? 

The data are owned by the Washington State Office of Financial Management (OFM), and are publicly available at https://ofm.wa.gov/washington-data-research/population-demographics/population-estimates. The population estimates data does not contain any identifying information and can be used without a data sharing agreement.  

How is the data created?  

Population estimates are calculated using methodology that varies depending on the availability of state and local area data. Data used to build these estimates include: 

• Federal decennial census counts, collected by the United States Census Bureau 

• Components of population change, such as births and death records, reported by Washington State Department of Health’s Vital Statistics program 

• Migration estimates based on administrative data sets such as school enrollment and tax filers’ data which reflect the mobility of the population 

• Other data that may reflect changes to the population, such as voter registrations, auto registrations, housing unit changes, occupancy rates, and average household sizes 

• Some city/town census results collected by municipal governments  

Who is included and excluded from the data?  

Population estimates reflect the resident population as defined by the U.S. Census Bureau. This includes persons in housing units, military personnel and their dependents, persons living in correctional institutions and persons living in residential care facilities. College students are considered residents of the place where they live while attending school. Seasonal populations, such as vacationers or migrant farmworkers, are counted at their usual place of residence. Persons with no usual place of residence are counted where they are located on April 1. 

What is included in the data? 

There are two forms of population estimate data provided by OFM. The first is the annual April 1 official population estimates. These estimates are available at the state, county, and city/town levels. The other available population estimates are the small area statistical estimates. These estimates are available for smaller areas and geographic areas that do not coincide with city or county boundaries, including census tracts, congressional and legislative districts, school districts, ZIP Codes, census blocks/block groups, and other geographies. Both sets of population estimates include the data subdivided by the following demographic characteristics: age, sex, race, and ethnicity. 

Why is the data created? 

OFM’s annual April 1 official population estimates are used in state program administration and in the allocation of selected state revenue. The small area population estimates are used for statistical and assessment purposes. Public Health-Seattle & King County uses the small area population estimates as denominators for rate calculations.   

How often is this data created? 

OFM’s annual April 1 official population estimates are calculated and released once per year. Small area population estimates are traditionally updated once a year in the fall. However, the small area estimates have not been updated since 2020 and no update is expected until 2023 or 2024. Each small area data delivery includes historical estimates, which may be updated from the prior year and are considered “living” estimates.  

What else is important to know about this data?  

Population estimates are approximations based on direct or indirect indicators and cannot be expected to be as accurate as a census.  

The Office of Financial Management (OFM) is currently working on updating its data and methods to release a full suite of population estimates incorporating the results from the 2020 Census. Changes and delays to the required inputs from the Census Bureau mean these estimates will likely not be available until late 2024. In the interim, the Washington State Department of Health and Public Health – Seattle & King County have developed a set of population estimates that incorporates the race/ethnicity by geography pattern from Census 2020 redistricting data into existing OFM data products. These Population Interim Estimates are an internally consistent set of demographic and geographic estimates from 2000 – 2022+. 

Where can I learn more about this data?  

• WA State Office of Financial Management population estimates website   

• State of Washington 2021 Population Trends (This report includes a section titled “Supplemental population information” that includes methodology descriptions.) 

• Download the April 1 official population estimates 

• Report on Population Estimate Accuracy 

• Small Area Demographic Estimates FAQ 

About data privacy and security 

The Assessment, Policy Development, and Evaluation Unit takes data security and the privacy of all individuals represented in our data very seriously. Data are stored in a secure environment.  For data sets that are not publicly available, only authorized staff are able to access them. Each data set has privacy guidelines to prevent sharing any information that may be identifiable – for example, not sharing (sometimes called suppressing) numbers when they are very small.