Median AQI
45
Good
Illinois · County air quality · 2025
Will County, Illinois
Median AQI 45 (Good). 59.3% of monitored days rated Good, direct from EPA Air Quality System stations.
- 45
- Median AQI
- 59.3%
- Good-air days
- 1
- Unhealthy days
- 13%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Will County's air is good on balance, among the more polluted 10% of US counties, a median AQI of 45 with 59.3% of 273 monitored days in the Good band, driven mainly by PM2.5.
- 45
- median AQI · Good
- 59.3%
- days rated Good
- PM2.5
- main pollutant
- 13%
- cleaner than US counties
1 day reached Unhealthy or worse; the worst single reading hit AQI 156.
Data updated July 2026
- Good · 162 d · 59.3%
- Moderate · 106 d · 38.8%
- USG · 4 d · 1.5%
- Unhealthy · 1 d · 0.4%
How did Will County's air break down in 2025?
Across 273 monitored days, 162 fell in the Good band (AQI 0–50) and 1 reached Unhealthy or worse. The worst single day peaked at AQI 156 (Unhealthy).
EPA AQS →Air quality data from EPA Air Quality System (2025). 273 days monitored. Median AQI: 45 (Good).
Insights: Will County, Illinois. EPA monitors recorded a median Air Quality Index of 45 across 273 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 162 (59%) fell in the Good band (AQI 0–50), 106 (39%) registered Moderate readings, and 4 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 74, while the worst single-day peak hit 156 (Unhealthy). Residents averaged about 17.8 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (168 days), Ozone (105 days). Across the 2020–2025 trend window, good days shifted by -21 and the median AQI moved -5 points, placing the multi-year trajectory at improving. Residents and visitors experienced 1 unhealthy-or-worse days combined, periods when the EPA recommends sensitive groups limit prolonged outdoor exertion. 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); Effingham (95.7% good, AQI 35).
Air Quality Summary
Good Days
59.3%
162 of 273 monitored days
-15.7pp vs 75% target
Max AQI Recorded
156
Unhealthy
Health Grade
Moderate
90th-pct AQI 74
Will County, Good days share 59.3%
National avg
Share of monitored days at AQI 0-50 (Good band).
Will County, Unhealthy-or-worse share 0.4%
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 273 monitored days across EPA AQI categories.
Good
162
59%
Moderate
106
39%
USG
4
1%
Unhealthy
1
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Will County.
- PM2.5 · 168 days · 61.5%
- Ozone · 105 days · 38.5%
Health Impact Assessment
Moderate
Will County's air quality is rated Moderate based on 59.3% good air days. There were 1 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 4 days reached "Unhealthy for Sensitive Groups" (AQI 101-150) and peak AQI reached 156. Sensitive groups should monitor real-time conditions at AirNow.gov.
The dominant pollutant is PM2.5, driving AQI on 168 of 273 monitored days.
5-Year Air Quality Trend
Air quality is improving in Will County. Best year: 2024 (245 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 183 | 176 | 3 | 1 | 50 | 156 |
| 2021 | 157 | 206 | 2 | 0 | 52 | 105 |
| 2022 | 193 | 170 | 2 | 0 | 49 | 101 |
| 2023 | 155 | 191 | 14 | 3 | 53 | 246 |
| 2024 | 245 | 120 | 0 | 0 | 44 | 84 |
| 2025 | 162 | 106 | 4 | 1 | 45 | 156 |
How does Will County compare?
How Will County compares
Good-day share worse than US avg
Will County 59.3%
Adams County, Illinois 94.4%
US average 76.5%
Median AQI worse than US avg
Will County 45
Adams County, Illinois 38
US average 38
Unhealthy days / yr worse than US avg
Will County 1
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 Will County.
Adair County, Oklahoma
AQI 45 · 59.2% good
Allen County, Indiana
AQI 45 · 58.2% good
Atascosa County, Texas
AQI 45 · 58.0% good
Baker County, Florida
AQI 45 · 69.1% good
Carson City County, Nevada
AQI 45 · 79.3% good
Clinton County, Iowa
AQI 45 · 59.9% good
What Will County's air means for you
On most days the air here is fine, but PM2.5 drives 1 unhealthy-or-worse day a year that sensitive groups should plan around.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-PM2.5 days, the guide explains what a median of 45 means for exposure. Health guidance
- See how Will County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Will County with its Illinois neighbours before drawing a conclusion about the region. All of Illinois
Based on 273 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 Will County, Illinois? ▼
Will County has a median Air Quality Index (AQI) of 45, rated "Good." 59.3% of monitored days (162 out of 273) had good air quality in 2025.
What is the main pollutant in Will County? ▼
The primary pollutant in Will County is Fine Particles (PM2.5), which was the main AQI driver on 168 days (62% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Will County have? ▼
In 2025, Will County recorded 1 unhealthy air days (1 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 156.
Is the air quality in Will County getting better or worse? ▼
Air quality in Will County is improving based on 5-year trends (2020-2025). Best year: 2024 with 245 good days. Worst year: 2023 with 155 good days.
What does AQI 45 mean for health? ▼
Will County's median AQI of 45 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 Will County compare to other counties in Illinois? ▼
Will County has 59.3% 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), Effingham (95.7% good).
What is the 90th percentile AQI in Will County? ▼
The 90th percentile AQI for Will County is 74, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 156 (Unhealthy).
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.