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 31 counties in 2015, at 100%. Denver County had the lowest, at 32.6%. The median was 77.3%. Source: EPA.

Highest100Fremont County

Lowest32.6Denver County

Median77.331 counties

Map of counties, 2015

Under 65
65 to 71
71 to 77
77 to 93
93 to 98
98 and over
No data

%, 2015. 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, 2015

%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

Rank	Counties	2015 (%)	Change on 2014
1	Fremont County	100	+1.7 pts
2	San Juan County	99.2	-0.8 pts
3	Delta County	99.1	-0.1 pts
4	Archuleta County	98.3	-1.4 pts
5	Routt County	98.1	+1.6 pts
6	Alamosa County	97.8	+3.3 pts
7	Pitkin County	97.6	-2.4 pts
8	Moffat County	97.2	+9.8 pts
9	Prowers County	96.6	+4.4 pts
10	Jackson County	95	+1.1 pts
11	Pueblo County	93	+4.3 pts
12	Grand County	92.2	n/a
13	San Miguel County	79.7	+4.9 pts
14	El Paso County	77.5	+2.7 pts
14	Gunnison County	77.5	-6.6 pts
16	Montezuma County	77.3	-0.8 pts
17	Park County	75.4	+6.8 pts
18	La Plata County	74.2	-2.2 pts
19	Adams County	72.9	+12.1 pts
20	Arapahoe County	71.2	-0.5 pts
20	Garfield County	71.2	-10.7 pts
22	Boulder County	69.3	-1.3 pts
23	Douglas County	68.5	+2.9 pts
24	Rio Blanco County	68.2	-4.1 pts
25	Jefferson County	66.8	+4.3 pts
26	Chaffee County	65	-3.7 pts
27	Clear Creek County	61.7	-1.6 pts
28	Mesa County	61.6	+2.4 pts
29	Weld County	61.4	-4.1 pts
30	Larimer County	48.5	-5.2 pts
31	Denver County	32.6	-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. 9 counties with data in other periods have no value for 2015 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), 2015) [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), 2015. 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=2015. 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), 2015. 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=2015.

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), 2015 [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=2015 (Accessed: 12 October 2026).

BibTeX

@misc{environmental_counties_in_colorado_by_2015,
  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), 2015}},
  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=2015. 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), 2015
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=2015
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/colorado-counties?period=2015.
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.

Embed code

<iframe src="https://invokely.ai/embed/rankings/good-air-quality-days-share/colorado-counties?period=2015" width="760" height="500" title="Counties in Colorado by share of days with good air quality (US EPA AQI), 2015, chart from Invokely" loading="lazy" style="border:0;width:100%;max-width:760px" referrerpolicy="strict-origin-when-cross-origin"></iframe>

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 2015, according to EPA.

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

Denver County, with 32.6% in 2015.

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. 9 counties have no value for 2015 and are not ranked.