Median AQI
35
Good
Illinois · County air quality · 2025
Effingham County, Illinois
Median AQI 35 (Good). 95.5% of monitored days rated Good, direct from EPA Air Quality System stations.
- 35
- Median AQI
- 95.5%
- Good-air days
- 0
- Unhealthy days
- 93%
- Cleaner than US counties
Effingham County's 2025 annual median AQI is 35 (Good), with 95.5% Good days
According to the U.S. EPA Air Quality System, Effingham County, Illinois posted a 2025 median AQI of 35 (Good) across 242 monitored days, with 95.5% 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
- Effingham County's 95.5% Good-day share places it cleaner than 93% of US counties in 2025.
- Closest median-AQI peer
- Atascosa County (76.0% Good, median AQI 35) is the closest nationwide median-AQI peer to Effingham County.
- 2020–2025 trend
- Effingham County's floor-qualifying Good-day share is stable from 2020 to 2025 (94.0% → 95.5%).
- Median AQI
- Median AQI: 35
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 95.5% of 242 monitored days in the Good band, driven mainly by Ozone.
- 35
- median AQI · Good
- 95.5%
- days rated Good
- Ozone
- main pollutant
- 93%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 84.
Annual release change
What changed in the 2025 EPA annual release
- Effingham County's Good-day share rose from 90.4% to 95.5% between the 2024 and 2025 EPA annual releases, a change of +5.0 percentage points.
- Effingham County's median AQI fell from 41 to 35 between the 2024 and 2025 EPA annual releases, a change of -6 points.
- Effingham County's peak single-day AQI fell from 101 to 84 between the 2024 and 2025 EPA annual releases, a change of -17 points.
Data updated August 2026
- Good · 231 d · 95.5%
- Moderate · 11 d · 4.5%
How did Effingham County's air break down in 2025?
Across 242 monitored days, 231 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 84 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 242 days monitored. Median AQI: 35 (Good).
Insights: Effingham County, Illinois. EPA monitors recorded a median Air Quality Index of 35 across 242 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), 11 (5%) 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 84 (Moderate). Residents averaged about 28.6 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (242 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by +1.5 points (measured against 166 monitored days in 2020 and 242 in 2025, so raw day counts are not comparable) 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 84, moderate but never Unhealthy. Nearby counties show comparable readings: Adams (94.7% good, AQI 38); Champaign (65.8% good, AQI 43); Clark (93.8% good, AQI 33); Cook (40.8% good, AQI 53); DuPage (63.8% good, AQI 42); Hamilton (67.9% good, AQI 42).
Air Quality Summary
Good Days
95.5%
231 of 242 monitored days
20.5pp vs 75% target
Max AQI Recorded
84
Moderate
Health Grade
Excellent
90th-pct AQI 46
Effingham County, Good days share 95.5%
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 242 monitored days across EPA AQI categories.
Good
231
95%
Moderate
11
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 Effingham County.
- Ozone · 242 days · 100.0%
Health Impact Assessment
Excellent
Effingham County's air quality is rated Excellent based on 95.5% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 95.5% 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 242 of 242 monitored days.
5-Year Air Quality Trend
Air quality is stable in Effingham County. Highest Good-day share: 2025 (95.5%, 231 of 242 monitored 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 | 231 | 11 | 0 | 0 | 35 | 84 |
How does Effingham County compare?
How Effingham County compares
Good-day share better than US avg
Effingham County 95.5%
Atascosa County, Texas 76.0%
US average 76.0%
Median AQI better than US avg
Effingham County 35
Atascosa County, Texas 35
US average 39
Unhealthy days / yr better than US avg
Effingham County 0
Atascosa County, Texas 0
US average 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Effingham County (35), not geographic neighbors.
Atascosa County, Texas
Median AQI 35 · 76.0% Good-day share
Benzie County, Michigan
Median AQI 35 · 91.1% Good-day share
Berkeley County, South Carolina
Median AQI 35 · 93.3% Good-day share
Boone County, Indiana
Median AQI 35 · 89.7% Good-day share
Brazoria County, Texas
Median AQI 35 · 80.8% Good-day share
Caroline County, Virginia
Median AQI 35 · 96.7% 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).
Polk County, Florida
95.5% Good-day share · median AQI 34
Sagadahoc County, Maine
95.4% Good-day share · median AQI 35
Mille Lacs County, Minnesota
95.3% Good-day share · median AQI 34
Taylor County, Wisconsin
95.3% Good-day share · median AQI 34
Jo Daviess County, Illinois
95.3% Good-day share · median AQI 33
Ascension County, Louisiana
95.6% 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 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 242 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 Effingham County, Illinois? ▼
Effingham County has a median Air Quality Index (AQI) of 35, rated "Good." 95.5% of monitored days (231 out of 242) 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 242 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 84.
Is the air quality in Effingham County getting better or worse? ▼
Air quality in Effingham County is stable across floor-qualifying years (2020-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2025 at 95.5% (231 of 242 days). Lowest qualifying Good-day share: 2023 at 75.2% (182 of 242 days).
What does AQI 35 mean for health? ▼
Effingham County's median AQI of 35 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Effingham County compare to other counties in Illinois? ▼
Effingham County has 95.5% good air days. Nearby counties in Illinois: Adams (94.7% good), Champaign (65.8% good), Clark (93.8% good), Cook (40.8% good), DuPage (63.8% good), Hamilton (67.9% 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 84 (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 Effingham 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.