Median AQI
35
Good
Illinois · County air quality · 2025
Effingham County, Illinois
Median AQI 35 (Good). 95.7% of monitored days rated Good, direct from EPA Air Quality System stations.
- 35
- Median AQI
- 95.7%
- Good-air days
- 0
- Unhealthy days
- 91%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Effingham County's air is good on balance, among the cleanest 10% of US counties, a median AQI of 35 with 95.7% of 211 monitored days in the Good band, driven mainly by Ozone.
- 35
- median AQI · Good
- 95.7%
- 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.
Data updated July 2026
- Good · 202 d · 95.7%
- Moderate · 9 d · 4.3%
How did Effingham County's air break down in 2025?
Across 211 monitored days, 202 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). 211 days monitored. Median AQI: 35 (Good).
Insights: Effingham County, Illinois. EPA monitors recorded a median Air Quality Index of 35 across 211 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 202 (96%) fell in the Good band (AQI 0–50), 9 (4%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 46, while the worst single-day peak hit 71 (Moderate). Residents averaged about 28.7 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (211 days). Across the 2020–2025 trend window, good days shifted by +46 and the median AQI moved -2 points, placing the multi-year trajectory at stable. The worst single reading over the 2020–2025 window was AQI 71, moderate but never Unhealthy. Nearby counties show comparable readings: Adams (94.4% good, AQI 38); Champaign (63.7% good, AQI 44); Clark (92.1% good, AQI 36); Cook (40.5% good, AQI 53); DuPage (61.2% good, AQI 44); Hamilton (66.5% good, AQI 43).
Air Quality Summary
Good Days
95.7%
202 of 211 monitored days
20.7pp vs 75% target
Max AQI Recorded
71
Moderate
Health Grade
Excellent
90th-pct AQI 46
Effingham County, Good days share 95.7%
National avg
Share of monitored days at AQI 0-50 (Good band).
Effingham 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 211 monitored days across EPA AQI categories.
Good
202
96%
Moderate
9
4%
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 Effingham County.
- Ozone · 211 days · 100.0%
Health Impact Assessment
Excellent
Effingham County's air quality is rated Excellent based on 95.7% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 95.7% of monitored days in 2025, with a median AQI of 35. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 211 of 211 monitored days.
5-Year Air Quality Trend
Air quality is stable in Effingham County. Best year: 2021 (226 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 156 | 10 | 0 | 0 | 37 | 84 |
| 2021 | 226 | 11 | 0 | 0 | 37 | 77 |
| 2022 | 215 | 24 | 0 | 0 | 38 | 100 |
| 2023 | 182 | 50 | 10 | 0 | 44 | 140 |
| 2024 | 217 | 22 | 1 | 0 | 41 | 101 |
| 2025 | 202 | 9 | 0 | 0 | 35 | 71 |
How does Effingham County compare?
How Effingham County compares
Good-day share better than US avg
Effingham County 95.7%
Adams County, Illinois 94.4%
US average 76.5%
Median AQI better than US avg
Effingham County 35
Adams County, Illinois 38
US average 38
Unhealthy days / yr about average
Effingham County 0
Adams 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 Effingham County.
Androscoggin County, Maine
AQI 35 · 85.5% good
Asotin County, Washington
AQI 35 · 73.8% good
Benton County, Washington
AQI 35 · 88.9% good
Benzie County, Michigan
AQI 35 · 91.1% good
Brooke County, West Virginia
AQI 35 · 79.3% good
Bucks County, Pennsylvania
AQI 35 · 87.5% good
What Effingham 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 35 means for exposure. Health guidance
- See how Effingham County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Effingham County with its Illinois neighbours before drawing a conclusion about the region. All of Illinois
Based on 211 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 Effingham County, Illinois? ▼
Effingham County has a median Air Quality Index (AQI) of 35, rated "Good." 95.7% of monitored days (202 out of 211) had good air quality in 2025.
What is the main pollutant in Effingham County? ▼
The primary pollutant in Effingham County is Ozone (O3), which was the main AQI driver on 211 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Effingham County have? ▼
In 2025, Effingham County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 71.
Is the air quality in Effingham County getting better or worse? ▼
Air quality in Effingham County is stable based on 5-year trends (2020-2025). Best year: 2021 with 226 good days. Worst year: 2020 with 156 good days.
What does AQI 35 mean for health? ▼
Effingham County's median AQI of 35 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 Effingham County compare to other counties in Illinois? ▼
Effingham County has 95.7% good air days. Nearby counties in Illinois: Adams (94.4% good), Champaign (63.7% good), Clark (92.1% good), Cook (40.5% good), DuPage (61.2% good), Hamilton (66.5% good).
What is the 90th percentile AQI in Effingham County? ▼
The 90th percentile AQI for Effingham County is 46, 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.