Median AQI
38
Good
Illinois · County air quality · 2025
Adams County, Illinois
Median AQI 38 (Good). 94.4% of monitored days rated Good, direct from EPA Air Quality System stations.
- 38
- Median AQI
- 94.4%
- Good-air days
- 0
- Unhealthy days
- 87%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Adams County's air is good on balance, cleaner than most US counties, a median AQI of 38 with 94.4% of 213 monitored days in the Good band, driven mainly by Ozone.
- 38
- median AQI · Good
- 94.4%
- days rated Good
- Ozone
- main pollutant
- 87%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 71.
Data updated July 2026
- Good · 201 d · 94.4%
- Moderate · 12 d · 5.6%
How did Adams County's air break down in 2025?
Across 213 monitored days, 201 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 71 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 213 days monitored. Median AQI: 38 (Good).
Insights: Adams County, Illinois. EPA monitors recorded a median Air Quality Index of 38 across 213 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 201 (94%) fell in the Good band (AQI 0–50), 12 (6%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 49, while the worst single-day peak hit 71 (Moderate). Residents averaged about 28.3 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (213 days). Across the 2020–2025 trend window, good days shifted by -19 and the median AQI moved +0 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 71, moderate but never Unhealthy. Nearby counties show comparable readings: Champaign (63.7% good, AQI 44); Clark (92.1% good, AQI 36); Cook (40.5% good, AQI 53); DuPage (61.2% good, AQI 44); Effingham (95.7% good, AQI 35); Hamilton (66.5% good, AQI 43).
Air Quality Summary
Good Days
94.4%
201 of 213 monitored days
19.4pp vs 75% target
Max AQI Recorded
71
Moderate
Health Grade
Excellent
90th-pct AQI 49
Adams County, Good days share 94.4%
National avg
Share of monitored days at AQI 0-50 (Good band).
Adams 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 213 monitored days across EPA AQI categories.
Good
201
94%
Moderate
12
6%
USG
0
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 Adams County.
- Ozone · 213 days · 100.0%
Health Impact Assessment
Excellent
Adams County's air quality is rated Excellent based on 94.4% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 94.4% of monitored days in 2025, with a median AQI of 38. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 213 of 213 monitored days.
5-Year Air Quality Trend
Air quality is improving in Adams County. Best year: 2022 (230 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 220 | 24 | 0 | 0 | 38 | 84 |
| 2021 | 219 | 23 | 0 | 0 | 40 | 93 |
| 2022 | 230 | 7 | 0 | 0 | 39 | 71 |
| 2023 | 184 | 49 | 12 | 0 | 43 | 136 |
| 2024 | 210 | 23 | 0 | 0 | 42 | 97 |
| 2025 | 201 | 12 | 0 | 0 | 38 | 71 |
How does Adams County compare?
How Adams County compares
Good-day share better than US avg
Adams County 94.4%
Champaign County, Illinois 63.7%
US average 76.5%
Median AQI about average
Adams County 38
Champaign County, Illinois 44
US average 38
Unhealthy days / yr about average
Adams County 0
Champaign County, Illinois 0
US average 0
Other Counties in Illinois
Air quality comparison for nearby counties in Illinois.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Adams County.
Anoka County, Minnesota
AQI 38 · 82.1% good
Atlantic County, New Jersey
AQI 38 · 79.6% good
Avery County, North Carolina
AQI 38 · 93.9% good
Barnstable County, Massachusetts
AQI 38 · 92.5% good
Bay County, Michigan
AQI 38 · 71.8% good
Becker County, Minnesota
AQI 38 · 84.7% good
What Adams 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 38 means for exposure. Health guidance
- See how Adams County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Adams County with its Illinois neighbours before drawing a conclusion about the region. All of Illinois
Based on 213 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 Adams County, Illinois? ▼
Adams County has a median Air Quality Index (AQI) of 38, rated "Good." 94.4% of monitored days (201 out of 213) had good air quality in 2025.
What is the main pollutant in Adams County? ▼
The primary pollutant in Adams County is Ozone (O3), which was the main AQI driver on 213 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Adams County have? ▼
In 2025, Adams County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 71.
Is the air quality in Adams County getting better or worse? ▼
Air quality in Adams County is improving based on 5-year trends (2020-2025). Best year: 2022 with 230 good days. Worst year: 2023 with 184 good days.
What does AQI 38 mean for health? ▼
Adams County's median AQI of 38 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 Adams County compare to other counties in Illinois? ▼
Adams County has 94.4% good air days. Nearby counties in Illinois: Champaign (63.7% good), Clark (92.1% good), Cook (40.5% good), DuPage (61.2% good), Effingham (95.7% good), Hamilton (66.5% good).
What is the 90th percentile AQI in Adams County? ▼
The 90th percentile AQI for Adams County is 49, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 71 (Moderate).
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.