Median AQI
42
Good
Illinois · County air quality · 2025
Jersey County, Illinois
Median AQI 42 (Good). 72.3% of monitored days rated Good, direct from EPA Air Quality System stations.
- 42
- Median AQI
- 72.3%
- Good-air days
- 1
- Unhealthy days
- 37%
- Cleaner than US counties
Jersey County's 2025 annual median AQI is 42 (Good), with 72.3% Good days
According to the U.S. EPA Air Quality System, Jersey County, Illinois posted a 2025 median AQI of 42 (Good) across 358 monitored days, with 72.3% rated Good and 1 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Jersey County's 72.3% Good-day share places it cleaner than 37% of US counties in 2025.
- Closest median-AQI peer
- Ada County (74.0% Good, median AQI 42) is the closest nationwide median-AQI peer to Jersey County.
- 2020–2025 trend
- Jersey County's floor-qualifying Good-day share is stable from 2020 to 2025 (72.1% → 72.3%).
- Median AQI
- Median AQI: 42
The verdict
According to EPA Air Quality System monitoring data, Jersey County's air is good on balance, more polluted than the median US county, a median AQI of 42 with 72.3% of 358 monitored days in the Good band, driven mainly by Ozone.
- 42
- median AQI · Good
- 72.3%
- days rated Good
- Ozone
- main pollutant
- 37%
- cleaner than US counties
1 day reached Unhealthy or worse; the worst single reading hit AQI 156.
Annual release change
What changed in the 2025 EPA annual release
- Jersey County's peak single-day AQI rose from 112 to 156 between the 2024 and 2025 EPA annual releases, a change of +44 points.
- Jersey County's Good-day share fell from 74.5% to 72.3% between the 2024 and 2025 EPA annual releases, a change of -2.1 percentage points.
- Jersey County's Unhealthy-category days rose from 0 to 1 between the 2024 and 2025 EPA annual releases, a change of +1 days.
Data updated August 2026
- Good · 259 d · 72.3%
- Moderate · 95 d · 26.5%
- USG · 3 d · 0.8%
- Unhealthy · 1 d · 0.3%
How did Jersey County's air break down in 2025?
Across 358 monitored days, 259 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). 358 days monitored. Median AQI: 42 (Good).
Insights: Jersey County, Illinois. EPA monitors recorded a median Air Quality Index of 42 across 358 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 259 (72%) fell in the Good band (AQI 0–50), 95 (27%) registered Moderate readings, and 3 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 67, while the worst single-day peak hit 156 (Unhealthy). Residents averaged about 21.7 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (190 days), PM2.5 (168 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by +0.3 points and the median AQI moved -2 points, placing the multi-year trajectory at stable. The annual record contains 1 day at Unhealthy or worse. On that day, the EPA recommends that sensitive groups limit prolonged outdoor exertion. 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); Effingham (95.5% good, AQI 35).
Air Quality Summary
Good Days
72.3%
259 of 358 monitored days
-2.7pp vs 75% target
Max AQI Recorded
156
Unhealthy
Health Grade
Moderate
90th-pct AQI 67
Jersey County, Good days share 72.3%
National avg
Share of monitored days at AQI 0-50 (Good band).
Jersey County, Unhealthy-or-worse share 2.8%
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 358 monitored days across EPA AQI categories.
Good
259
72%
Moderate
95
27%
USG
3
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 Jersey County.
- Ozone · 190 days · 53.1%
- PM2.5 · 168 days · 46.9%
Health Impact Assessment
Moderate
Jersey County's air quality is rated Moderate based on 72.3% good air days. There were 1 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 3 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 Ozone, driving AQI on 190 of 358 monitored days.
5-Year Air Quality Trend
Air quality is stable in Jersey County. Highest Good-day share: 2024 (74.5%, 248 of 333 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 258 | 99 | 1 | 0 | 44 | 112 |
| 2021 | 225 | 133 | 2 | 0 | 45 | 112 |
| 2022 | 240 | 120 | 5 | 0 | 45 | 112 |
| 2023 | 199 | 148 | 17 | 1 | 48 | 166 |
| 2024 | 248 | 84 | 1 | 0 | 42 | 112 |
| 2025 | 259 | 95 | 3 | 1 | 42 | 156 |
How does Jersey County compare?
How Jersey County compares
Good-day share worse than typical
Jersey County 72.3%
Ada County, Idaho 74.0%
Typical US county 76.0%
Median AQI worse than typical
Jersey County 42
Ada County, Idaho 42
Typical US county 39
Unhealthy days / yr about typical
Jersey County 1
Ada County, Idaho 0
Typical US county 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Jersey County (42), not geographic neighbors.
Ada County, Idaho
Median AQI 42 · 74.0% Good-day share
Adams County, Pennsylvania
Median AQI 42 · 74.4% Good-day share
Allen County, Ohio
Median AQI 42 · 67.0% Good-day share
Asotin County, Washington
Median AQI 42 · 61.9% Good-day share
Baldwin County, Alabama
Median AQI 42 · 75.5% Good-day share
Bell County, Kentucky
Median AQI 42 · 67.0% 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).
Dodge County, Wisconsin
72.3% Good-day share · median AQI 40
Carbon County, Utah
72.3% Good-day share · median AQI 44
Gunnison County, Colorado
72.5% Good-day share · median AQI 46
Bartholomew County, Indiana
72.6% Good-day share · median AQI 43
Ingham County, Michigan
72.6% Good-day share · median AQI 38
Mercer County, Pennsylvania
72.6% Good-day share · median AQI 42
Illinois counties on the map
Geographic containment only, other monitored counties in Illinois, independent of AQI or pollutant match.
What Jersey County's air means for you
On most days the air here is fine, but Ozone 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-Ozone days, the guide explains what a median of 42 means for exposure. Health guidance
- See how Jersey County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Jersey County with its Illinois neighbours before drawing a conclusion about the region. All of Illinois
Based on 358 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 Jersey County, Illinois? ▼
Jersey County has a median Air Quality Index (AQI) of 42, rated "Good." 72.3% of monitored days (259 out of 358) had good air quality in 2025.
What is the main pollutant in Jersey County? ▼
The primary pollutant in Jersey County is Ozone (O3), which was the main AQI driver on 190 days (53% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Jersey County have? ▼
In 2025, Jersey County recorded 1 unhealthy air days (1 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 156.
Is the air quality in Jersey County getting better or worse? ▼
Air quality in Jersey 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: 2024 at 74.5% (248 of 333 days). Lowest qualifying Good-day share: 2023 at 54.5% (199 of 365 days).
What does AQI 42 mean for health? ▼
Jersey County's median AQI of 42 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Jersey County compare to other counties in Illinois? ▼
Jersey County has 72.3% 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), Effingham (95.5% good).
What is the 90th percentile AQI in Jersey County? ▼
The 90th percentile AQI for Jersey County is 67, 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. Spotted a figure that looks wrong? Report a correction.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files for Jersey 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.