# Counties in Colorado by median Air Quality Index (US EPA), 2025

All 30 values come from U.S. Environmental Protection Agency for 2025, so the places are comparable. 10 counties have no value for that period and are not ranked.

- Indicator id: `aqi_median`
- Unit: index
- Definition: 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. 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.
- Source: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: median daily AQI (https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual)
- Publisher page: https://invokely.ai/en/publishers/environmental-protection-agency
- Retrieved: 2026-10-12
- Citation: 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.
- Web page: https://invokely.ai/rankings/median-air-quality-index/colorado-counties

| Rank | Place | index |
|---:|---|---:|
| 1 | Weld County | 52 |
| 2 | Denver County | 50 |
| 2 | Larimer County | 50 |
| 4 | Adams County | 49 |
| 5 | Arapahoe County | 48 |
| 5 | Boulder County | 48 |
| 5 | Chaffee County | 48 |
| 5 | Clear Creek County | 48 |
| 5 | Jefferson County | 48 |
| 5 | La Plata County | 48 |
| 5 | Park County | 48 |
| 12 | Garfield County | 47 |
| 13 | Douglas County | 46 |
| 13 | El Paso County | 46 |
| 13 | Gilpin County | 46 |
| 13 | Gunnison County | 46 |
| 13 | Mesa County | 46 |
| 18 | Montezuma County | 45 |
| 18 | Pueblo County | 45 |
| 20 | Grand County | 44 |
| 21 | San Miguel County | 36 |
| 22 | Archuleta County | 34 |
| 23 | Delta County | 29 |
| 24 | Prowers County | 27 |
| 25 | Alamosa County | 25 |
| 26 | Fremont County | 23 |
| 27 | Routt County | 22 |
| 28 | Pitkin County | 19 |
| 29 | San Juan County | 12 |
| 30 | Jackson County | 9 |