# Counties in Colorado by highest daily 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_max`
- Unit: index
- Definition: Highest daily Air Quality Index (AQI) value recorded in a US county during the year, from the EPA AirData annual summaries. Values above 500 are beyond the AQI scale and are published as EPA computes them.
- Source: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: highest 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: highest daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
- Web page: https://invokely.ai/rankings/highest-daily-air-quality-index/colorado-counties

| Rank | Place | index |
|---:|---|---:|
| 1 | Prowers County | 652 |
| 2 | Pitkin County | 154 |
| 3 | Garfield County | 131 |
| 4 | Douglas County | 122 |
| 5 | Boulder County | 119 |
| 5 | Jefferson County | 119 |
| 5 | Larimer County | 119 |
| 5 | Weld County | 119 |
| 9 | Archuleta County | 115 |
| 9 | Denver County | 115 |
| 9 | Gunnison County | 115 |
| 12 | Adams County | 112 |
| 12 | La Plata County | 112 |
| 14 | Chaffee County | 108 |
| 15 | Park County | 105 |
| 16 | Delta County | 103 |
| 17 | Arapahoe County | 101 |
| 17 | Gilpin County | 101 |
| 17 | Montezuma County | 101 |
| 17 | Pueblo County | 101 |
| 21 | Clear Creek County | 100 |
| 22 | El Paso County | 97 |
| 22 | Mesa County | 97 |
| 24 | San Miguel County | 94 |
| 25 | Routt County | 87 |
| 26 | Fremont County | 77 |
| 26 | Grand County | 77 |
| 28 | Alamosa County | 76 |
| 29 | San Juan County | 57 |
| 30 | Jackson County | 56 |