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)

Fremont County had the highest share of days with good air quality (US EPA AQI) of 32 counties in 2016, at 100%. Denver County had the lowest, at 34.7%. The median was 77.6%. Source: EPA.

Keep it in a collection in your library.
Highest100Fremont County
Lowest34.7Denver County
Median77.632 counties

Map of counties, 2016

Adams County: 64.5 %Alamosa County: 98.3 %Arapahoe County: 71.3 %Archuleta County: 98.8 %Boulder County: 87.3 %Chaffee County: 64.2 %Clear Creek County: 67.5 %Delta County: 98.3 %Denver County: 34.7 %Douglas County: 69.3 %El Paso County: 69.1 %Fremont County: 100 %Garfield County: 71.9 %Grand County: 86.2 %Gunnison County: 86.3 %Jackson County: 99.1 %Jefferson County: 66.9 %La Plata County: 65 %Larimer County: 44.3 %Mesa County: 66.9 %Moffat County: 91.6 %Montezuma County: 78.1 %Montrose County: 93.3 %Park County: 73.8 %Pitkin County: 100 %Prowers County: 98 %Pueblo County: 94.5 %Rio Blanco County: 74 %Routt County: 97.4 %San Juan County: 100 %San Miguel County: 77.1 %Weld County: 54.9 %
  • Under 65
  • 65 to 70
  • 70 to 78
  • 78 to 93
  • 93 to 98
  • 98 and over
  • No data
%, 2016. 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, 2016

Fremont County: 100 %Fremont County100Pitkin County: 100 %Pitkin County100San Juan County: 100 %San Juan County100Jackson County: 99.1 %Jackson County99.1Archuleta County: 98.8 %Archuleta County98.8Alamosa County: 98.3 %Alamosa County98.3Delta County: 98.3 %Delta County98.3Prowers County: 98 %Prowers County98Routt County: 97.4 %Routt County97.4Pueblo County: 94.5 %Pueblo County94.5Montrose County: 93.3 %Montrose County93.3Moffat County: 91.6 %Moffat County91.6Boulder County: 87.3 %Boulder County87.3Gunnison County: 86.3 %Gunnison County86.3Grand County: 86.2 %Grand County86.2Montezuma County: 78.1 %Montezuma County78.1San Miguel County: 77.1 %San Miguel County77.1Rio Blanco County: 74 %Rio Blanco County74Park County: 73.8 %Park County73.8Garfield County: 71.9 %Garfield County71.9Arapahoe County: 71.3 %Arapahoe County71.3Douglas County: 69.3 %Douglas County69.3El Paso County: 69.1 %El Paso County69.1Clear Creek County: 67.5 %Clear Creek County67.5Jefferson County: 66.9 %Jefferson County66.9Mesa County: 66.9 %Mesa County66.9La Plata County: 65 %La Plata County65Adams County: 64.5 %Adams County64.5Chaffee County: 64.2 %Chaffee County64.2Weld County: 54.9 %Weld County54.9Larimer County: 44.3 %Larimer County44.3Denver County: 34.7 %Denver County34.7Fremont County: 100 %Fremont County100Pitkin County: 100 %Pitkin County100San Juan County: 100 %San Juan County100Jackson County: 99.1 %Jackson County99.1Archuleta County: 98.8 %Archuleta County98.8Alamosa County: 98.3 %Alamosa County98.3Delta County: 98.3 %Delta County98.3Prowers County: 98 %Prowers County98Routt County: 97.4 %Routt County97.4Pueblo County: 94.5 %Pueblo County94.5Montrose County: 93.3 %Montrose County93.3Moffat County: 91.6 %Moffat County91.6Boulder County: 87.3 %Boulder County87.3Gunnison County: 86.3 %Gunnison County86.3Grand County: 86.2 %Grand County86.2Montezuma County: 78.1 %Montezuma County78.1San Miguel County: 77.1 %San Miguel County77.1Rio Blanco County: 74 %Rio Blanco County74Park County: 73.8 %Park County73.8Garfield County: 71.9 %Garfield County71.9Arapahoe County: 71.3 %Arapahoe County71.3Douglas County: 69.3 %Douglas County69.3El Paso County: 69.1 %El Paso County69.1Clear Creek County: 67.5 %Clear Creek County67.5Jefferson County: 66.9 %Jefferson County66.9Mesa County: 66.9 %Mesa County66.9La Plata County: 65 %La Plata County65Adams County: 64.5 %Adams County64.5Chaffee County: 64.2 %Chaffee County64.2Weld County: 54.9 %Weld County54.9Larimer County: 44.3 %Larimer County44.3Denver County: 34.7 %Denver County34.7
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2016 (%)Change on 2015
1Fremont County1000 pts
1Pitkin County100+2.4 pts
1San Juan County100+0.8 pts
4Jackson County99.1+4.1 pts
5Archuleta County98.8+0.5 pts
6Alamosa County98.3+0.5 pts
6Delta County98.3-0.8 pts
8Prowers County98+1.4 pts
9Routt County97.4-0.7 pts
10Pueblo County94.5+1.5 pts
11Montrose County93.3n/a
12Moffat County91.6-5.6 pts
13Boulder County87.3+18 pts
14Gunnison County86.3+8.8 pts
15Grand County86.2-6 pts
16Montezuma County78.1+0.8 pts
17San Miguel County77.1-2.6 pts
18Rio Blanco County74+5.8 pts
19Park County73.8-1.6 pts
20Garfield County71.9+0.7 pts
21Arapahoe County71.3+0.1 pts
22Douglas County69.3+0.8 pts
23El Paso County69.1-8.4 pts
24Clear Creek County67.5+5.8 pts
25Jefferson County66.9+0.1 pts
25Mesa County66.9+5.3 pts
27La Plata County65-9.2 pts
28Adams County64.5-8.4 pts
29Chaffee County64.2-0.8 pts
30Weld County54.9-6.5 pts
31Larimer County44.3-4.2 pts
32Denver County34.7+2.1 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. 8 counties with data in other periods have no value for 2016 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), 2016) [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), 2016. 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=2016. 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), 2016. 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=2016.

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), 2016 [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=2016 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_colorado_by_2016,
  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), 2016}},
  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=2016. 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), 2016
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=2016
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/colorado-counties?period=2016.
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  -
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 share of days with good air quality (US EPA AQI) using official data, and cite the source.
rank_places {"indicator":"aqi_good_days_share","level":"province","within":"Colorado","limit":10}
GET https://invokely.ai/api/v1/rank?indicator=aqi_good_days_share&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 share of days with good air quality (US EPA AQI)?

Fremont County, with 100% in 2016, according to EPA.

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

Denver County, with 34.7% in 2016.

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. 8 counties have no value for 2016 and are not ranked.

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

Counties in Colorado: more rankings