Median AQI
38
Good
Illinois · County air quality · 2025
Adams County, Illinois
Median AQI 38 (Good). 94.7% of monitored days rated Good, direct from EPA Air Quality System stations.
- 38
- Median AQI
- 94.7%
- Good-air days
- 0
- Unhealthy days
- 91%
- Cleaner than US counties
Adams County's 2025 annual median AQI is 38 (Good), with 94.7% Good days
According to the U.S. EPA Air Quality System, Adams County, Illinois posted a 2025 median AQI of 38 (Good) across 244 monitored days, with 94.7% rated Good and 0 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Adams County's 94.7% Good-day share places it cleaner than 91% of US counties in 2025.
- Closest median-AQI peer
- Albemarle County (81.0% Good, median AQI 38) is the closest nationwide median-AQI peer to Adams County.
- 2020–2025 trend
- Adams County's floor-qualifying Good-day share is improving from 2020 to 2025 (90.2% → 94.7%).
- Median AQI
- Median AQI: 38
The verdict
According to EPA Air Quality System monitoring data, Adams County's air is good on balance, among the cleanest 10% of US counties, a median AQI of 38 with 94.7% of 244 monitored days in the Good band, driven mainly by Ozone.
- 38
- median AQI · Good
- 94.7%
- days rated Good
- Ozone
- main pollutant
- 91%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 71.
Annual release change
What changed in the 2025 EPA annual release
- Adams County's Good-day share rose from 90.1% to 94.7% between the 2024 and 2025 EPA annual releases, a change of +4.5 percentage points.
- Adams County's peak single-day AQI fell from 97 to 71 between the 2024 and 2025 EPA annual releases, a change of -26 points.
- Adams County's median AQI fell from 42 to 38 between the 2024 and 2025 EPA annual releases, a change of -4 points.
Data updated August 2026
- Good · 231 d · 94.7%
- Moderate · 13 d · 5.3%
How did Adams County's air break down in 2025?
Across 244 monitored days, 231 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). 244 days monitored. Median AQI: 38 (Good).
Insights: Adams County, Illinois. EPA monitors recorded a median Air Quality Index of 38 across 244 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 231 (95%) fell in the Good band (AQI 0–50), 13 (5%) 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 28.4 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (244 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by +4.5 points 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 (65.8% good, AQI 43); Clark (93.8% good, AQI 33); Cook (40.8% good, AQI 53); DuPage (63.8% good, AQI 42); Effingham (95.5% good, AQI 35); Hamilton (67.9% good, AQI 42).
Air Quality Summary
Good Days
94.7%
231 of 244 monitored days
19.7pp vs 75% target
Max AQI Recorded
71
Moderate
Health Grade
Excellent
90th-pct AQI 49
Adams County, Good days share 94.7%
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 244 monitored days across EPA AQI categories.
Good
231
95%
Moderate
13
5%
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 · 244 days · 100.0%
Health Impact Assessment
Excellent
Adams County's air quality is rated Excellent based on 94.7% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 94.7% 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 244 of 244 monitored days.
5-Year Air Quality Trend
Air quality is improving in Adams County. Highest Good-day share: 2022 (97.0%, 230 of 237 monitored 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 | 231 | 13 | 0 | 0 | 38 | 71 |
How does Adams County compare?
How Adams County compares
Good-day share better than typical
Adams County 94.7%
Albemarle County, Virginia 81.0%
Typical US county 76.0%
Median AQI better than typical
Adams County 38
Albemarle County, Virginia 38
Typical US county 39
Unhealthy days / yr better than typical
Adams County 0
Albemarle County, Virginia 0
Typical US county 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Adams County (38), not geographic neighbors.
Albemarle County, Virginia
Median AQI 38 · 81.0% Good-day share
Alexander County, North Carolina
Median AQI 38 · 93.5% Good-day share
Amador County, California
Median AQI 38 · 87.4% Good-day share
Anoka County, Minnesota
Median AQI 38 · 74.1% Good-day share
Avery County, North Carolina
Median AQI 38 · 92.3% Good-day share
Becker County, Minnesota
Median AQI 38 · 74.0% Good-day share
Same primary pollutant: Ozone
Ozone led the AQI on the most monitored days here. These peers share that driver and the closest Good-day share (a second relationship type beyond median-AQI neighbors).
Morgan County, Kentucky
94.7% Good-day share · median AQI 35
Jefferson County, New York
94.7% Good-day share · median AQI 34
Rockdale County, Georgia
94.6% Good-day share · median AQI 36
Lauderdale County, Mississippi
94.6% Good-day share · median AQI 35
Calvert County, Maryland
94.6% Good-day share · median AQI 38
Polk County, Texas
94.8% Good-day share · median AQI 33
Illinois counties on the map
Geographic containment only, other monitored counties in Illinois, independent of AQI or pollutant match.
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 244 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
Keep exploring the annual AQI record
Air-quality reading list
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." 94.7% of monitored days (231 out of 244) 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 244 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 across floor-qualifying years (2020-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2022 at 97.0% (230 of 237 days). Lowest qualifying Good-day share: 2023 at 75.1% (184 of 245 days).
What does AQI 38 mean for health? ▼
Adams County's median AQI of 38 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Adams County compare to other counties in Illinois? ▼
Adams County has 94.7% good air days. Nearby counties in Illinois: Champaign (65.8% good), Clark (93.8% good), Cook (40.8% good), DuPage (63.8% good), Effingham (95.5% good), Hamilton (67.9% 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. Spotted a figure that looks wrong? Report a correction.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files for Adams County, Illinois · 2020–2025
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Every figure on PlainAirData 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.