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

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

San Juan County had the highest share of days with good air quality (US EPA AQI) of 30 counties in 2023, at 100%. Denver County had the lowest, at 35.9%. The median was 67.6%. Source: EPA.

Keep it in a collection in your library.
Highest100San Juan County
Lowest35.9Denver County
Median67.630 counties

Map of counties, 2023

Adams County: 49 %Alamosa County: 86.1 %Arapahoe County: 65.5 %Archuleta County: 95.6 %Boulder County: 52.6 %Chaffee County: 39.8 %Clear Creek County: 56.8 %Denver County: 35.9 %Douglas County: 54.9 %El Paso County: 65.8 %Fremont County: 99.4 %Garfield County: 45.5 %Gilpin County: 70.7 %Grand County: 82.9 %Gunnison County: 69.1 %Jackson County: 79.2 %Jefferson County: 56.4 %La Plata County: 64.9 %Larimer County: 47.9 %Mesa County: 67.4 %Montezuma County: 79.7 %Park County: 50.9 %Pitkin County: 99.2 %Prowers County: 96 %Pueblo County: 76.5 %Rio Blanco County: 67.7 %Routt County: 98.6 %San Juan County: 100 %San Miguel County: 73.1 %Weld County: 40 %
  • Under 49
  • 49 to 57
  • 57 to 68
  • 68 to 77
  • 77 to 96
  • 96 and over
  • No data
%, 2023. 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, 2023

San Juan County: 100 %San Juan County100Fremont County: 99.4 %Fremont County99.4Pitkin County: 99.2 %Pitkin County99.2Routt County: 98.6 %Routt County98.6Prowers County: 96 %Prowers County96Archuleta County: 95.6 %Archuleta County95.6Alamosa County: 86.1 %Alamosa County86.1Grand County: 82.9 %Grand County82.9Montezuma County: 79.7 %Montezuma County79.7Jackson County: 79.2 %Jackson County79.2Pueblo County: 76.5 %Pueblo County76.5San Miguel County: 73.1 %San Miguel County73.1Gilpin County: 70.7 %Gilpin County70.7Gunnison County: 69.1 %Gunnison County69.1Rio Blanco County: 67.7 %Rio Blanco County67.7Mesa County: 67.4 %Mesa County67.4El Paso County: 65.8 %El Paso County65.8Arapahoe County: 65.5 %Arapahoe County65.5La Plata County: 64.9 %La Plata County64.9Clear Creek County: 56.8 %Clear Creek County56.8Jefferson County: 56.4 %Jefferson County56.4Douglas County: 54.9 %Douglas County54.9Boulder County: 52.6 %Boulder County52.6Park County: 50.9 %Park County50.9Adams County: 49 %Adams County49Larimer County: 47.9 %Larimer County47.9Garfield County: 45.5 %Garfield County45.5Weld County: 40 %Weld County40Chaffee County: 39.8 %Chaffee County39.8Denver County: 35.9 %Denver County35.9San Juan County: 100 %San Juan County100Fremont County: 99.4 %Fremont County99.4Pitkin County: 99.2 %Pitkin County99.2Routt County: 98.6 %Routt County98.6Prowers County: 96 %Prowers County96Archuleta County: 95.6 %Archuleta County95.6Alamosa County: 86.1 %Alamosa County86.1Grand County: 82.9 %Grand County82.9Montezuma County: 79.7 %Montezuma County79.7Jackson County: 79.2 %Jackson County79.2Pueblo County: 76.5 %Pueblo County76.5San Miguel County: 73.1 %San Miguel County73.1Gilpin County: 70.7 %Gilpin County70.7Gunnison County: 69.1 %Gunnison County69.1Rio Blanco County: 67.7 %Rio Blanco County67.7Mesa County: 67.4 %Mesa County67.4El Paso County: 65.8 %El Paso County65.8Arapahoe County: 65.5 %Arapahoe County65.5La Plata County: 64.9 %La Plata County64.9Clear Creek County: 56.8 %Clear Creek County56.8Jefferson County: 56.4 %Jefferson County56.4Douglas County: 54.9 %Douglas County54.9Boulder County: 52.6 %Boulder County52.6Park County: 50.9 %Park County50.9Adams County: 49 %Adams County49Larimer County: 47.9 %Larimer County47.9Garfield County: 45.5 %Garfield County45.5Weld County: 40 %Weld County40Chaffee County: 39.8 %Chaffee County39.8Denver County: 35.9 %Denver County35.9
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2023 (%)Change on 2022
1San Juan County100+3.4 pts
2Fremont County99.4+1.9 pts
3Pitkin County99.2+2.5 pts
4Routt County98.6-1.4 pts
5Prowers County96+2.8 pts
6Archuleta County95.6+9.8 pts
7Alamosa County86.1-6.1 pts
8Grand County82.9+4.7 pts
9Montezuma County79.7-2.5 pts
10Jackson County79.2-12.3 pts
11Pueblo County76.5-14.3 pts
12San Miguel County73.1-3 pts
13Gilpin County70.7-7.7 pts
14Gunnison County69.1-7.9 pts
15Rio Blanco County67.7+1.1 pts
16Mesa County67.4-9.9 pts
17El Paso County65.8-2.4 pts
18Arapahoe County65.5+0.6 pts
19La Plata County64.9-8 pts
20Clear Creek County56.8-11.2 pts
21Jefferson County56.4-7.7 pts
22Douglas County54.9-11.4 pts
23Boulder County52.6-8.8 pts
24Park County50.9-15 pts
25Adams County49-0.3 pts
26Larimer County47.9-0.3 pts
27Garfield County45.5-15 pts
28Weld County40-6.6 pts
29Chaffee County39.8-23 pts
30Denver County35.9-8.2 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. 10 counties with data in other periods have no value for 2023 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 Colorado by share of days with good air quality (US EPA AQI), 2023) [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 Colorado by share of days with good air quality (US EPA AQI), 2023. 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/colorado-counties?period=2023. 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 Colorado by share of days with good air quality (US EPA AQI), 2023. 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/colorado-counties?period=2023.

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 Colorado by share of days with good air quality (US EPA AQI), 2023 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/good-air-quality-days-share/colorado-counties?period=2023 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_colorado_by_2023,
  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 Colorado by share of days with good air quality (US EPA AQI), 2023}},
  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/colorado-counties?period=2023. 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 Colorado by share of days with good air quality (US EPA AQI), 2023
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/colorado-counties?period=2023
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/colorado-counties?period=2023.
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)?

San Juan County, with 100% in 2023, according to EPA.

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

Denver County, with 35.9% in 2023.

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. 10 counties have no value for 2023 and are not ranked.

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

Counties in Colorado: more rankings