Data / Rankings / Median Air Quality Index (US EPA) / Counties in Colorado

Counties in Colorado by median Air Quality Index (US EPA)

Denver County had the highest median Air Quality Index (US EPA) of 31 counties in 2019, at 54. Jackson County had the lowest, at 8. The median was 46. Source: the U.S. Environmental Protection Agency.

Keep it in a collection in your library.
Highest54Denver County
Lowest8Jackson County
Median4631 counties

Map of counties, 2019

Adams County: 50 indexAlamosa County: 12 indexArapahoe County: 47 indexArchuleta County: 31 indexBoulder County: 50 indexChaffee County: 50 indexClear Creek County: 47 indexDelta County: 41 indexDenver County: 54 indexDouglas County: 47 indexEl Paso County: 46 indexFremont County: 13 indexGarfield County: 48 indexGilpin County: 45 indexGrand County: 45 indexGunnison County: 46 indexJackson County: 8 indexJefferson County: 46 indexLa Plata County: 44 indexLarimer County: 50 indexMesa County: 47 indexMontezuma County: 46 indexPark County: 50 indexPitkin County: 11 indexProwers County: 14 indexPueblo County: 26 indexRio Blanco County: 47 indexRoutt County: 13 indexSan Juan County: 9 indexSan Miguel County: 45 indexWeld County: 53 index
  • Under 13
  • 13 to 44
  • 44 to 46
  • 46 to 47
  • 47 to 50
  • 50 and over
  • No data
index, 2019. Hatched areas have no value for this period. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2019

Denver County: 54 indexDenver County54Weld County: 53 indexWeld County53Adams County: 50 indexAdams County50Boulder County: 50 indexBoulder County50Chaffee County: 50 indexChaffee County50Larimer County: 50 indexLarimer County50Park County: 50 indexPark County50Garfield County: 48 indexGarfield County48Arapahoe County: 47 indexArapahoe County47Clear Creek County: 47 indexClear Creek County47Douglas County: 47 indexDouglas County47Mesa County: 47 indexMesa County47Rio Blanco County: 47 indexRio Blanco County47El Paso County: 46 indexEl Paso County46Gunnison County: 46 indexGunnison County46Jefferson County: 46 indexJefferson County46Montezuma County: 46 indexMontezuma County46Gilpin County: 45 indexGilpin County45Grand County: 45 indexGrand County45San Miguel County: 45 indexSan Miguel County45La Plata County: 44 indexLa Plata County44Delta County: 41 indexDelta County41Archuleta County: 31 indexArchuleta County31Pueblo County: 26 indexPueblo County26Prowers County: 14 indexProwers County14Fremont County: 13 indexFremont County13Routt County: 13 indexRoutt County13Alamosa County: 12 indexAlamosa County12Pitkin County: 11 indexPitkin County11San Juan County: 9 indexSan Juan County9Jackson County: 8 indexJackson County8Denver County: 54 indexDenver County54Weld County: 53 indexWeld County53Adams County: 50 indexAdams County50Boulder County: 50 indexBoulder County50Chaffee County: 50 indexChaffee County50Larimer County: 50 indexLarimer County50Park County: 50 indexPark County50Garfield County: 48 indexGarfield County48Arapahoe County: 47 indexArapahoe County47Clear Creek County: 47 indexClear Creek County47Douglas County: 47 indexDouglas County47Mesa County: 47 indexMesa County47Rio Blanco County: 47 indexRio Blanco County47El Paso County: 46 indexEl Paso County46Gunnison County: 46 indexGunnison County46Jefferson County: 46 indexJefferson County46Montezuma County: 46 indexMontezuma County46Gilpin County: 45 indexGilpin County45Grand County: 45 indexGrand County45San Miguel County: 45 indexSan Miguel County45La Plata County: 44 indexLa Plata County44Delta County: 41 indexDelta County41Archuleta County: 31 indexArchuleta County31Pueblo County: 26 indexPueblo County26Prowers County: 14 indexProwers County14Fremont County: 13 indexFremont County13Routt County: 13 indexRoutt County13Alamosa County: 12 indexAlamosa County12Pitkin County: 11 indexPitkin County11San Juan County: 9 indexSan Juan County9Jackson County: 8 indexJackson County8
index. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Retrieved 2026-10-12.

Full ranking

RankCounties2019
index		Change on 2018
1Denver County540
2Weld County53-1
3Adams County50-4
3Boulder County50+1
3Chaffee County50-8
3Larimer County50-3
3Park County50-1
8Garfield County480
9Arapahoe County47+1
9Clear Creek County47-4
9Douglas County47-2
9Mesa County47-2
9Rio Blanco County470
14El Paso County46-1
14Gunnison County46-1
14Jefferson County460
14Montezuma County46+2
18Gilpin County45n/a
18Grand County45-2
18San Miguel County45-1
21La Plata County44-1
22Delta County41+5
23Archuleta County31-7
24Pueblo County26-3
25Prowers County14-2
26Fremont County13-2
26Routt County13-2
28Alamosa County12-7
29Pitkin County11-4
30San Juan County9-1
31Jackson County8-1

Other periods

About this ranking

Median of the daily Air Quality Index (AQI) values of a US county over the days of the year with an AQI, from the EPA AirData annual summaries.

More on how it is measured
  • The daily county AQI is the highest AQI among the monitors and pollutants reported that day (ozone, PM2.5, PM10, carbon monoxide and nitrogen dioxide).
  • Lower is cleaner: 0 to 50 is good, 51 to 100 moderate and above 100 unhealthy for sensitive groups.

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. 9 counties with data in other periods have no value for 2019 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: median daily AQI. 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: median daily AQI (Counties in Colorado by median Air Quality Index (US EPA), 2019) [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: median daily AQI, Counties in Colorado by median Air Quality Index (US EPA), 2019. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/median-air-quality-index/colorado-counties?period=2019. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: median daily AQI. Counties in Colorado by median Air Quality Index (US EPA), 2019. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/median-air-quality-index/colorado-counties?period=2019.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: median daily AQI, Counties in Colorado by median Air Quality Index (US EPA), 2019 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/median-air-quality-index/colorado-counties?period=2019 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_colorado_by_2019,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: median daily AQI: Counties in Colorado by median Air Quality Index (US EPA), 2019}},
  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/median-air-quality-index/colorado-counties?period=2019. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. 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: median daily AQI: Counties in Colorado by median Air Quality Index (US EPA), 2019
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/median-air-quality-index/colorado-counties?period=2019
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/median-air-quality-index/colorado-counties?period=2019.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
ER  -
Embed this chart

Paste this code into a web page or a blog post. The chart shows the latest figures as they are published, with the source and a link back to this page.

Sites that read oEmbed links, such as WordPress, can show the chart when you paste the link to this page.

Use this data in your AI agent

Invokely serves this figure to AI assistants through MCP and to code through a REST API, with the source and citation attached. Ask your assistant:

Rank Counties in Colorado by median Air Quality Index (US EPA) using official data, and cite the source.
rank_places {"indicator":"aqi_median","level":"province","within":"Colorado","limit":10}
GET https://invokely.ai/api/v1/rank?indicator=aqi_median&level=province&within=Colorado&limit=10

Connect Claude, ChatGPT or Cursor in one step. The trial answers 25 calls a day without an account.

Questions

Which county has the highest median Air Quality Index (US EPA)?

Denver County, with 54 in 2019, according to the U.S. Environmental Protection Agency.

Which county has the lowest median Air Quality Index (US EPA)?

Jackson County, with 8 in 2019.

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: median daily AQI. Retrieved 2026-10-12. 9 counties have no value for 2019 and are not ranked.

Median Air Quality Index (US EPA): other rankings

Counties in Colorado: more rankings