Data / Rankings / Share of days with good air quality (US EPA AQI) / Counties in Washington

Counties in Washington by share of days with good air quality (US EPA AQI)

Kitsap County had the highest share of days with good air quality (US EPA AQI) of 30 counties in 2017, at 90.6%. Okanogan County had the lowest, at 45.8%. The median was 77.8%. Source: EPA.

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Highest90.6Kitsap County
Lowest45.8Okanogan County
Median77.830 counties

Map of counties, 2017

Adams County: 88.5 %Asotin County: 65.1 %Benton County: 66.3 %Chelan County: 64.7 %Clallam County: 67.4 %Clark County: 72.3 %Columbia County: 74.8 %Cowlitz County: 82.5 %Franklin County: 78.9 %Garfield County: 78.7 %Grant County: 77.5 %Grays Harbor County: 85.8 %Jefferson County: 89.9 %King County: 53.2 %Kitsap County: 90.6 %Kittitas County: 66.2 %Klickitat County: 88.2 %Lewis County: 82.7 %Mason County: 82.9 %Okanogan County: 45.8 %Pierce County: 66.3 %Skagit County: 89 %Snohomish County: 66.8 %Spokane County: 62.2 %Stevens County: 53.4 %Thurston County: 79.1 %Walla Walla County: 78.1 %Whatcom County: 86.2 %Whitman County: 81.9 %Yakima County: 52.9 %
  • Under 64
  • 64 to 67
  • 67 to 78
  • 78 to 82
  • 82 to 87
  • 87 and over
  • No data
%, 2017. Hatched areas have no value for this period. Source: Invokely calculation with data from EPA. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2017

Kitsap County: 90.6 %Kitsap County90.6Jefferson County: 89.9 %Jefferson County89.9Skagit County: 89 %Skagit County89Adams County: 88.5 %Adams County88.5Klickitat County: 88.2 %Klickitat County88.2Whatcom County: 86.2 %Whatcom County86.2Grays Harbor County: 85.8 %Grays Harbor County85.8Mason County: 82.9 %Mason County82.9Lewis County: 82.7 %Lewis County82.7Cowlitz County: 82.5 %Cowlitz County82.5Whitman County: 81.9 %Whitman County81.9Thurston County: 79.1 %Thurston County79.1Franklin County: 78.9 %Franklin County78.9Garfield County: 78.7 %Garfield County78.7Walla Walla County: 78.1 %Walla Walla County78.1Grant County: 77.5 %Grant County77.5Columbia County: 74.8 %Columbia County74.8Clark County: 72.3 %Clark County72.3Clallam County: 67.4 %Clallam County67.4Snohomish County: 66.8 %Snohomish County66.8Benton County: 66.3 %Benton County66.3Pierce County: 66.3 %Pierce County66.3Kittitas County: 66.2 %Kittitas County66.2Asotin County: 65.1 %Asotin County65.1Chelan County: 64.7 %Chelan County64.7Spokane County: 62.2 %Spokane County62.2Stevens County: 53.4 %Stevens County53.4King County: 53.2 %King County53.2Yakima County: 52.9 %Yakima County52.9Okanogan County: 45.8 %Okanogan County45.8Kitsap County: 90.6 %Kitsap County90.6Jefferson County: 89.9 %Jefferson County89.9Skagit County: 89 %Skagit County89Adams County: 88.5 %Adams County88.5Klickitat County: 88.2 %Klickitat County88.2Whatcom County: 86.2 %Whatcom County86.2Grays Harbor County: 85.8 %Grays Harbor County85.8Mason County: 82.9 %Mason County82.9Lewis County: 82.7 %Lewis County82.7Cowlitz County: 82.5 %Cowlitz County82.5Whitman County: 81.9 %Whitman County81.9Thurston County: 79.1 %Thurston County79.1Franklin County: 78.9 %Franklin County78.9Garfield County: 78.7 %Garfield County78.7Walla Walla County: 78.1 %Walla Walla County78.1Grant County: 77.5 %Grant County77.5Columbia County: 74.8 %Columbia County74.8Clark County: 72.3 %Clark County72.3Clallam County: 67.4 %Clallam County67.4Snohomish County: 66.8 %Snohomish County66.8Benton County: 66.3 %Benton County66.3Pierce County: 66.3 %Pierce County66.3Kittitas County: 66.2 %Kittitas County66.2Asotin County: 65.1 %Asotin County65.1Chelan County: 64.7 %Chelan County64.7Spokane County: 62.2 %Spokane County62.2Stevens County: 53.4 %Stevens County53.4King County: 53.2 %King County53.2Yakima County: 52.9 %Yakima County52.9Okanogan County: 45.8 %Okanogan County45.8
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2017 (%)Change on 2016
1Kitsap County90.6-6 pts
2Jefferson County89.9-6.7 pts
3Skagit County89-1.4 pts
4Adams County88.5-9.5 pts
5Klickitat County88.2-4.4 pts
6Whatcom County86.2-6.1 pts
7Grays Harbor County85.8-4.9 pts
8Mason County82.9-6.4 pts
9Lewis County82.7-10.2 pts
10Cowlitz County82.5-8.7 pts
11Whitman County81.9-12.1 pts
12Thurston County79.1-9.2 pts
13Franklin County78.9-16.9 pts
14Garfield County78.7n/a
15Walla Walla County78.1-6.4 pts
16Grant County77.5-16.1 pts
17Columbia County74.8-20.4 pts
18Clark County72.3-10.8 pts
19Clallam County67.4-8.8 pts
20Snohomish County66.8-9.2 pts
21Benton County66.3-17.6 pts
21Pierce County66.3-7.2 pts
23Kittitas County66.2-12.5 pts
24Asotin County65.1-12.2 pts
25Chelan County64.7-12.9 pts
26Spokane County62.2-7.2 pts
27Stevens County53.4-16 pts
28King County53.2-12.4 pts
29Yakima County52.9-4.8 pts
30Okanogan County45.8-14.9 pts

Other periods

About this ranking

Days with a daily Air Quality Index of 0 to 50 (good) as a percentage of the days of the year with an AQI in a US county. Calculated by Invokely from the day counts in the EPA AirData annual summaries; both counts are stored with each value.

United States counties with air quality monitors only, about 1,000 of some 3,100 in recent years; a county without monitors has no value. The number of days with an AQI differs between counties because some monitors run only in the ozone season.

Every value in the ranking comes from the same publisher and the same period, so the counties are compared on one definition. 4 counties with data in other periods have no value for 2017 and are left out rather than filled from another source. Equal values share a rank.

How to cite

U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.

Citation styles

The publisher is the author. Invokely is named only as the place the figures were read, where a style asks for it.

APA 7

U.S. Environmental Protection Agency. (2026). EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts (Counties in Washington by share of days with good air quality (US EPA AQI), 2017) [Data set]. Retrieved October 12, 2026, from https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual

MLA 9

EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts, Counties in Washington by share of days with good air quality (US EPA AQI), 2017. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/good-air-quality-days-share/washington-counties?period=2017. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. Counties in Washington by share of days with good air quality (US EPA AQI), 2017. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/good-air-quality-days-share/washington-counties?period=2017.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts, Counties in Washington by share of days with good air quality (US EPA AQI), 2017 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/good-air-quality-days-share/washington-counties?period=2017 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_washington_by_2017,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts: Counties in Washington by share of days with good air quality (US EPA AQI), 2017}},
  year = {2026},
  howpublished = {Data set},
  url = {https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual},
  urldate = {2026-10-12},
  note = {Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/washington-counties?period=2017. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. https://aqs.epa.gov/aqsweb/airdata/download\_files.html\#Annual. Retrieved 2026-10-12.},
}
RIS
TY  - DATA
AU  - U.S. Environmental Protection Agency
TI  - EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts: Counties in Washington by share of days with good air quality (US EPA AQI), 2017
PY  - 2026
DA  - 2026/07/13
PB  - U.S. Environmental Protection Agency
DB  - Invokely
UR  - https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual
L2  - https://invokely.ai/rankings/good-air-quality-days-share/washington-counties?period=2017
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/washington-counties?period=2017.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
ER  -
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Questions

Which county has the highest share of days with good air quality (US EPA AQI)?

Kitsap County, with 90.6% in 2017, according to EPA.

Which county has the lowest share of days with good air quality (US EPA AQI)?

Okanogan County, with 45.8% in 2017.

Where does this ranking come from?

Every value comes from one source and one period, so the places are comparable: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. Retrieved 2026-10-12. 4 counties have no value for 2017 and are not ranked.

Share of days with good air quality (US EPA AQI): other rankings

Counties in Washington: more rankings