King County, WA Population by Age

The median age in King County, WA is 37.3, as per 2019-2023 ACS 5 -Year Estimates. Of the total population, 16.47% were under the age of 15, 19.99% aged 15 to 29, 49.78% aged 30 to 64, 12.01% aged 65 to 84, and 1.74% were 85 years of age and older.
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Updated Feb 22, 2025

King County, WA population age distributions

A complete breakdown of King County's age demographics from 0 to 85 years, distributed across 18 age groups is listed in the table below.

Age Group Population % of Total Population
Under 5 years 120,412 5.32%
5 to 9 years 124,058 5.48%
10 to 14 years 128,232 5.67%
15 to 19 years 123,346 5.45%
20 to 24 years 132,192 5.84%
25 to 29 years 196,893 8.7%
30 to 34 years 215,322 9.52%
35 to 39 years 192,285 8.5%
40 to 44 years 166,013 7.34%
45 to 49 years 148,443 6.56%
50 to 54 years 145,042 6.41%
55 to 59 years 132,462 5.85%
60 to 64 years 126,645 5.6%
65 to 69 years 104,423 4.61%
70 to 74 years 83,321 3.68%
75 to 79 years 51,598 2.28%
80 to 84 years 32,634 1.44%
85 years and over 39,392 1.74%
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King County, WA population by age group

Key stats
628,240
Population under 25 years
770,513
Population aged 25-44
552,592
Population aged 45-64
311,368
Population aged 65+

Sources: U.S. Census Bureau, American Community Survey (ACS) 2019-2023

FIGURE 1

King County, WA population by age group.

The largest age group is 30 to 34 years with a population of 215,322 (9.52% of the total population).

Source: U.S. Census Bureau American Community Survey (ACS) 2019-2023 5-Year Estimates.

The largest age group in King County, WA was for the group of age 30 to 34 years with a population of 215,322 (9.52%), according to the 2019-2023 American Community Survey.

At the same time, the smallest age group in King County, WA was the 80 to 84 years with a population of 32,634 (1.44%).

King County, WA population by age cohort

To better understand the age distribution of King County, WA's population, we divided it into the following 3 cohorts:

  • Children : Under the age of 18 years
  • Adults (working population): Between the age of 18 and 64 years
  • Seniors: 65 years and above

FIGURE 2

King County, WA population by age cohort

The largest age group was 18 to 64 years with a population of 1.5 million (66.48% of the total population).

Source: U.S. Census Bureau American Community Survey (ACS) 2019-2023 5-Year Estimates.

King County, WA population by age cohort

Here's the population for each of the three cohorts.

Age Group Population % of Total Population
Under 18 years 447,121 19.76%
18 to 64 years 1,504,224 66.48%
65 years and over 311,368 13.76%
Exploring King County's Diversity? Request Customized Data Now!

Key stats for each age cohort as per our analysis of U.S. Census Bureau American Community Survey:

  • King County 's population under 18 was 19.76%, compared to the 22.16% nationwide.
  • King County's working population (between 18 and 64) was 66.48%, compared to 61% nationwide.
  • King County's elderly or the senior population (over 65 age) was 13.76% as compared to 16.84% nationwide.

King County, WA population pyramid

Population pyramid for King County, WA is charted below using the estimates from U.S. Census Bureau's American Community Survey 5-Year estimates. A wide base suggests population increase, narrow base indicates declining birth rates.

Key stats from our analysis of the King County's population pyramid:

  • Youth dependency ratio, which is the number of children aged 0-14 per 100 persons aged 15-64, for King County, WA, is 23.6.
  • Old-age dependency ratio, which is the number of persons aged 65 or over per 100 persons aged 15-64, for King County, WA, is 19.7.
  • Total dependency ratio for King County, WA is 43.3.
  • Potential support ratio, which is the number of youth (working age population) per elderly, for King County, WA is 5.1.

FIGURE 3

King County, WA population pyramid

King County population distrubution across age and gender. A wide base suggests population increase, narrow base indicates declining birth rates.

Source: U.S. Census Bureau American Community Survey (ACS) 2019-2023 5-Year Estimates.

King County, WA population pyramid

Here's the King County, WA's male and female population across different age groups .

Age Group Population(Male) Population(Female) Total Population
Under 5 years 61,683 58,729 120,412
5 to 9 years 64,149 59,909 124,058
10 to 14 years 64,743 63,489 128,232
15 to 19 years 62,343 61,003 123,346
20 to 24 years 67,362 64,830 132,192
25 to 29 years 102,829 94,064 196,893
30 to 34 years 113,597 101,725 215,322
35 to 39 years 101,111 91,174 192,285
40 to 44 years 85,735 80,278 166,013
45 to 49 years 76,190 72,253 148,443
50 to 54 years 74,788 70,254 145,042
55 to 59 years 67,265 65,197 132,462
60 to 64 years 63,803 62,842 126,645
65 to 69 years 50,583 53,840 104,423
70 to 74 years 38,489 44,832 83,321
75 to 79 years 23,353 28,245 51,598
80 to 84 years 13,898 18,736 32,634
85 years and over 14,336 25,056 39,392
Exploring King County's Diversity? Request Customized Data Now!

Things to know

What is the population of King County, WA under 18?

King County's population under the age of 18 is 447,121, as per the latest U.S. Census Bureau's American Community Survey estimates. This population is 19.76% of the total resident population of King County, WA.

What is the aging population in King County, WA?

King County's population aged 65 years and above was 311,368. As per the U.S. Census Bureau's American Community Survey, this population is 13.76% of the entire population.

References

Datasets

Explore datasets by year of publication.
2025
King County, WA Age Group Population Dataset: A Complete Breakdown of King County Age Demographics from 0 to 85 Years and Over, Distributed Across 18 Age Groups // 2025 Edition
Last updated February 22, 2025
ACS
Free
Neilsberg
CSV, JSON
2019-2023
CC BY 4.0
About this dataset

Context

The dataset tabulates the King County population distribution across 18 age groups. It lists the population in each age group along with the percentage population relative of the total population for King County. The dataset can be utilized to understand the population distribution of King County by age. For example, using this dataset, we can identify the largest age group in King County.

Key observations

The largest age group in King County, WA was for the group of age 30 to 34 years years with a population of 215,322 (9.52%), according to the ACS 2019-2023 5-Year Estimates. At the same time, the smallest age group in King County, WA was the 80 to 84 years years with a population of 32,634 (1.44%). Source: U.S. Census Bureau American Community Survey (ACS) 2019-2023 5-Year Estimates

Content

When available, the data consists of estimates from the U.S. Census Bureau American Community Survey (ACS) 2019-2023 5-Year Estimates

Age groups:

  • Under 5 years
  • 5 to 9 years
  • 10 to 14 years
  • 15 to 19 years
  • 20 to 24 years
  • 25 to 29 years
  • 30 to 34 years
  • 35 to 39 years
  • 40 to 44 years
  • 45 to 49 years
  • 50 to 54 years
  • 55 to 59 years
  • 60 to 64 years
  • 65 to 69 years
  • 70 to 74 years
  • 75 to 79 years
  • 80 to 84 years
  • 85 years and over

Variables / Data Columns

  • Age Group: This column displays the age group in consideration
  • Population: The population for the specific age group in the King County is shown in this column.
  • % of Total Population: This column displays the population of each age group as a proportion of King County total population. Please note that the sum of all percentages may not equal one due to rounding of values.

Good to know

Margin of Error

Data in the dataset are based on the estimates and are subject to sampling variability and thus a margin of error. Neilsberg Research recommends using caution when presening these estimates in your research.

Custom data

If you do need custom data for any of your research project, report or presentation, you can contact our research staff at research@neilsberg.com for a feasibility of a custom tabulation on a fee-for-service basis.

Inspiration

Neilsberg Research Team curates, analyze and publishes demographics and economic data from a variety of public and proprietary sources, each of which often includes multiple surveys and programs. The large majority of Neilsberg Research aggregated datasets and insights is made available for free download at https://www.neilsberg.com/research/.

Recommended for further research

This dataset is a part of the main dataset for King County Population by Age. You can refer the same here

King County, WA Age Cohorts Dataset: Children, Working Adults, and Seniors in King County - Population and Percentage Analysis // 2025 Edition
Last updated February 22, 2025
ACS
Free
Neilsberg
CSV, JSON
2019-2023
CC BY 4.0
About this dataset

Context

The dataset tabulates the King County population by age cohorts (Children: Under 18 years; Working population: 18-64 years; Senior population: 65 years or more). It lists the population in each age cohort group along with its percentage relative to the total population of King County. The dataset can be utilized to understand the population distribution across children, working population and senior population for dependency ratio, housing requirements, ageing, migration patterns etc.

Key observations

The largest age group was 18 to 64 years with a poulation of 1.5 million (66.48% of the total population). Source: U.S. Census Bureau American Community Survey (ACS) 2019-2023 5-Year Estimates.

Content

When available, the data consists of estimates from the U.S. Census Bureau American Community Survey (ACS) 2019-2023 5-Year Estimates.

Age cohorts:

  • Under 18 years
  • 18 to 64 years
  • 65 years and over

Variables / Data Columns

  • Age Group: This column displays the age cohort for the King County population analysis. Total expected values are 3 groups ( Children, Working Population and Senior Population).
  • Population: The population for the age cohort in King County is shown in the following column.
  • Percent of Total Population: The population as a percent of total population of the King County is shown in the following column.

Good to know

Margin of Error

Data in the dataset are based on the estimates and are subject to sampling variability and thus a margin of error. Neilsberg Research recommends using caution when presening these estimates in your research.

Custom data

If you do need custom data for any of your research project, report or presentation, you can contact our research staff at research@neilsberg.com for a feasibility of a custom tabulation on a fee-for-service basis.

Inspiration

Neilsberg Research Team curates, analyze and publishes demographics and economic data from a variety of public and proprietary sources, each of which often includes multiple surveys and programs. The large majority of Neilsberg Research aggregated datasets and insights is made available for free download at https://www.neilsberg.com/research/.

Recommended for further research

This dataset is a part of the main dataset for King County Population by Age. You can refer the same here

King County, WA Population Pyramid Dataset: Age Groups, Male and Female Population, and Total Population for Demographics Analysis // 2025 Edition
Last updated February 22, 2025
ACS
Free
Neilsberg
CSV, JSON
2019-2023
CC BY 4.0
About this dataset

Context

The dataset tabulates the data for the King County, WA population pyramid, which represents the King County population distribution across age and gender, using estimates from the U.S. Census Bureau American Community Survey (ACS) 2019-2023 5-Year Estimates. It lists the male and female population for each age group, along with the total population for those age groups. Higher numbers at the bottom of the table suggest population growth, whereas higher numbers at the top indicate declining birth rates. Furthermore, the dataset can be utilized to understand the youth dependency ratio, old-age dependency ratio, total dependency ratio, and potential support ratio.

Key observations

  • Youth dependency ratio, which is the number of children aged 0-14 per 100 persons aged 15-64, for King County, WA, is 23.6.
  • Old-age dependency ratio, which is the number of persons aged 65 or over per 100 persons aged 15-64, for King County, WA, is 19.7.
  • Total dependency ratio for King County, WA is 43.3.
  • Potential support ratio, which is the number of youth (working age population) per elderly, for King County, WA is 5.1.
Content

When available, the data consists of estimates from the U.S. Census Bureau American Community Survey (ACS) 2019-2023 5-Year Estimates.

Age groups:

  • Under 5 years
  • 5 to 9 years
  • 10 to 14 years
  • 15 to 19 years
  • 20 to 24 years
  • 25 to 29 years
  • 30 to 34 years
  • 35 to 39 years
  • 40 to 44 years
  • 45 to 49 years
  • 50 to 54 years
  • 55 to 59 years
  • 60 to 64 years
  • 65 to 69 years
  • 70 to 74 years
  • 75 to 79 years
  • 80 to 84 years
  • 85 years and over

Variables / Data Columns

  • Age Group: This column displays the age group for the King County population analysis. Total expected values are 18 and are define above in the age groups section.
  • Population (Male): The male population in the King County for the selected age group is shown in the following column.
  • Population (Female): The female population in the King County for the selected age group is shown in the following column.
  • Total Population: The total population of the King County for the selected age group is shown in the following column.

Good to know

Margin of Error

Data in the dataset are based on the estimates and are subject to sampling variability and thus a margin of error. Neilsberg Research recommends using caution when presening these estimates in your research.

Custom data

If you do need custom data for any of your research project, report or presentation, you can contact our research staff at research@neilsberg.com for a feasibility of a custom tabulation on a fee-for-service basis.

Inspiration

Neilsberg Research Team curates, analyze and publishes demographics and economic data from a variety of public and proprietary sources, each of which often includes multiple surveys and programs. The large majority of Neilsberg Research aggregated datasets and insights is made available for free download at https://www.neilsberg.com/research/.

Recommended for further research

This dataset is a part of the main dataset for King County Population by Age. You can refer the same here

If you're looking for datasets from another year, please feel free to contact us at research@neilsberg.com and we'll be happy to assist you further.

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Neilsberg Research
Neilsberg Research team are data scientists with expertise in processing, analysis and visualization of big data helping small businesses make right decisions.

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