Counties in Colorado by share of days with good air quality (US EPA AQI), 2025

Jackson County had the highest share of days with good air quality (US EPA AQI) of 30 counties in 2025, at 98.9%. Weld County had the lowest, at 44.7%. The median was 70.8%. Source: EPA.

Highest98.9Jackson County

Lowest44.7Weld County

Median70.830 counties

Map of counties, 2025

Under 58
58 to 66
66 to 71
71 to 81
81 to 92
92 and over
No data

%, 2025. 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, 2025

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

Full ranking

Rank	Counties	2025 (%)	Change on 2024
1	Jackson County	98.9	+15.4 pts
1	San Juan County	98.9	-0.3 pts
3	Routt County	93.7	-6 pts
4	Fremont County	93.4	-4.4 pts
5	Prowers County	92.6	+4.9 pts
6	Pitkin County	92.3	-3.4 pts
7	Alamosa County	91.5	+2.5 pts
8	Delta County	85.6	n/a
9	Archuleta County	83	-12.4 pts
9	San Miguel County	83	-3.1 pts
11	Grand County	79.7	-2.9 pts
12	Gilpin County	75.8	+9.7 pts
13	Montezuma County	75.1	+3.5 pts
14	Pueblo County	73.4	+5.4 pts
15	Gunnison County	72.5	+6.1 pts
16	Garfield County	69	+10 pts
17	El Paso County	68.2	+13 pts
18	Clear Creek County	67.9	+10.4 pts
19	Douglas County	67.7	+10.4 pts
20	Chaffee County	66	+20 pts
21	Mesa County	65.2	+6.5 pts
22	Park County	63.1	+9.8 pts
23	La Plata County	60.8	-5.3 pts
24	Jefferson County	58.9	+6.4 pts
25	Boulder County	58.4	+0.5 pts
26	Arapahoe County	58.1	+4.5 pts
27	Adams County	55.1	+14.9 pts
28	Larimer County	50.7	+8.1 pts
29	Denver County	50.4	+15.2 pts
30	Weld County	44.7	+4 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 2025 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), 2025) [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), 2025. 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. 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), 2025. 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.

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), 2025 [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 (Accessed: 12 October 2026).

BibTeX

@misc{environmental_counties_in_colorado_by_2025,
  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), 2025}},
  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. 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), 2025
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
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/colorado-counties.
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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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}
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Questions

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

Jackson County, with 98.9% in 2025, according to EPA.

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

Weld County, with 44.7% in 2025.

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 2025 and are not ranked.