Population Estimates Data Biography
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). Most population estimates are publicly available. We also work directly with OFM to acquire estimates for some combinations of multiple demographic characteristics that may not be posted online. The population estimates data do 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, 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. 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.
Where can I learn more about this data?
2025 Population Trends (This report includes a section titled “Supplemental information” that includes methodology descriptions.)
About data privacy and security
Public Health – Seattle-King County takes data security and the privacy of all individuals represented in our data very seriously. Identifiable data are stored securely, and only authorized staff can access the data, and only for approved uses. To prevent individuals from being identified in the results of data analyses, information is not shared when the number of people who are in a category is very small.
Questions?
Visit our Frequently Asked Questions page for additional support.
If you have more questions, or if you are unable to access any of the links in a data biography, you may contact us at data.request@kingcounty.gov.