Median AQI
48
Good
Colorado · County air quality · 2025
Gilpin County, Colorado
Median AQI 48 (Good). 68.5% of monitored days rated Good, direct from EPA Air Quality System stations.
- 48
- Median AQI
- 68.5%
- Good-air days
- 0
- Unhealthy days
- 29%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Gilpin County's air is good on balance, more polluted than the median US county, a median AQI of 48 with 68.5% of 270 monitored days in the Good band, driven mainly by Ozone.
- 48
- median AQI · Good
- 68.5%
- days rated Good
- Ozone
- main pollutant
- 29%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 101.
Data updated July 2026
- Good · 185 d · 68.5%
- Moderate · 84 d · 31.1%
- USG · 1 d · 0.4%
How did Gilpin County's air break down in 2025?
Across 270 monitored days, 185 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 101 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 270 days monitored. Median AQI: 48 (Good).
Insights: Gilpin County, Colorado. EPA monitors recorded a median Air Quality Index of 48 across 270 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 185 (69%) fell in the Good band (AQI 0–50), 84 (31%) registered Moderate readings, and 1 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 71, while the worst single-day peak hit 101 (USG). Residents averaged about 20.6 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (270 days). Across the 2020–2025 trend window, good days shifted by -93 and the median AQI moved +3 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 101, usg but never Unhealthy. Nearby counties show comparable readings: Adams (50.2% good, AQI 50); Alamosa (90.8% good, AQI 24); Arapahoe (47.3% good, AQI 51); Archuleta (79.5% good, AQI 32); Boulder (50.9% good, AQI 50); Clear Creek (64.4% good, AQI 48).
Air Quality Summary
Good Days
68.5%
185 of 270 monitored days
-6.5pp vs 75% target
Max AQI Recorded
101
USG
Health Grade
Moderate
90th-pct AQI 71
Gilpin County, Good days share 68.5%
National avg
Share of monitored days at AQI 0-50 (Good band).
Gilpin County, Unhealthy-or-worse share 0.0%
National avg
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
AQI Day Breakdown (2025)
Distribution of 270 monitored days across EPA AQI categories.
Good
185
69%
Moderate
84
31%
USG
1
0%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Gilpin County.
- Ozone · 270 days · 100.0%
Health Impact Assessment
Moderate
Gilpin County's air quality is rated Moderate based on 68.5% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 68.5% of monitored days in 2025, with a median AQI of 48. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 270 of 270 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Gilpin County. Best year: 2022 (286 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 278 | 70 | 9 | 0 | 45 | 136 |
| 2021 | 250 | 94 | 18 | 1 | 46 | 151 |
| 2022 | 286 | 75 | 4 | 0 | 45 | 112 |
| 2023 | 258 | 103 | 4 | 0 | 47 | 129 |
| 2024 | 240 | 111 | 12 | 0 | 48 | 150 |
| 2025 | 185 | 84 | 1 | 0 | 48 | 101 |
How does Gilpin County compare?
How Gilpin County compares
Good-day share worse than US avg
Gilpin County 68.5%
Adams County, Colorado 50.2%
US average 76.5%
Median AQI worse than US avg
Gilpin County 48
Adams County, Colorado 50
US average 38
Unhealthy days / yr about average
Gilpin County 0
Adams County, Colorado 0
US average 0
Other Counties in Colorado
Air quality comparison for nearby counties in Colorado.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Gilpin County.
Black Hawk County, Iowa
AQI 48 · 56.6% good
Box Elder County, Utah
AQI 48 · 60.0% good
Brookings County, South Dakota
AQI 48 · 53.0% good
Clear Creek County, Colorado
AQI 48 · 64.4% good
Coconino County, Arizona
AQI 48 · 62.5% good
Columbia County, Florida
AQI 48 · 56.4% good
What Gilpin County's air means for you
The air here stays in the breathable range year-round, with Ozone the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 48 means for exposure. Health guidance
- See how Gilpin County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Gilpin County with its Colorado neighbours before drawing a conclusion about the region. All of Colorado
Based on 270 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
More Air Quality Data
Air Quality Guides
Frequently Asked Questions
What is the air quality in Gilpin County, Colorado? ▼
Gilpin County has a median Air Quality Index (AQI) of 48, rated "Good." 68.5% of monitored days (185 out of 270) had good air quality in 2025.
What is the main pollutant in Gilpin County? ▼
The primary pollutant in Gilpin County is Ozone (O3), which was the main AQI driver on 270 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Gilpin County have? ▼
In 2025, Gilpin County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 101.
Is the air quality in Gilpin County getting better or worse? ▼
Air quality in Gilpin County is worsening based on 5-year trends (2020-2025). Best year: 2022 with 286 good days. Worst year: 2025 with 185 good days.
What does AQI 48 mean for health? ▼
Gilpin County's median AQI of 48 falls in the "Good" category. See the <a href="/guides/understanding-aqi" class="underline">AQI category guide</a> for what each range means for health.
How does Gilpin County compare to other counties in Colorado? ▼
Gilpin County has 68.5% good air days. Nearby counties in Colorado: Adams (50.2% good), Alamosa (90.8% good), Arapahoe (47.3% good), Archuleta (79.5% good), Boulder (50.9% good), Clear Creek (64.4% good).
What is the 90th percentile AQI in Gilpin County? ▼
The 90th percentile AQI for Gilpin County is 71, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 101 (USG).
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025 (aqs.epa.gov). For current conditions (not shown here — this page is historical annual data), see EPA AirNow (airnow.gov). See our methodology for how AQI, median, and coverage figures are computed.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer.
Every figure on PlainAir is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.