Median AQI
35
Good
Illinois · County air quality · 2025
Jo Daviess County, Illinois
Median AQI 35 (Good). 94.3% of monitored days rated Good, direct from EPA Air Quality System stations.
- 35
- Median AQI
- 94.3%
- Good-air days
- 0
- Unhealthy days
- 86%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Jo Daviess County's air is good on balance, cleaner than most US counties, a median AQI of 35 with 94.3% of 228 monitored days in the Good band, driven mainly by Ozone.
- 35
- median AQI · Good
- 94.3%
- days rated Good
- Ozone
- main pollutant
- 86%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 87.
Data updated July 2026
- Good · 215 d · 94.3%
- Moderate · 13 d · 5.7%
How did Jo Daviess County's air break down in 2025?
Across 228 monitored days, 215 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 87 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 228 days monitored. Median AQI: 35 (Good).
Insights: Jo Daviess County, Illinois. EPA monitors recorded a median Air Quality Index of 35 across 228 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 215 (94%) fell in the Good band (AQI 0–50), 13 (6%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 47, while the worst single-day peak hit 87 (Moderate). Residents averaged about 28.3 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (228 days). Across the 2020–2025 trend window, good days shifted by -122 and the median AQI moved +3 points, placing the multi-year trajectory at stable. The worst single reading over the 2020–2025 window was AQI 87, 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); Effingham (95.7% good, AQI 35).
Air Quality Summary
Good Days
94.3%
215 of 228 monitored days
19.3pp vs 75% target
Max AQI Recorded
87
Moderate
Health Grade
Excellent
90th-pct AQI 47
Jo Daviess County, Good days share 94.3%
National avg
Share of monitored days at AQI 0-50 (Good band).
Jo Daviess 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 228 monitored days across EPA AQI categories.
Good
215
94%
Moderate
13
6%
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 Jo Daviess County.
- Ozone · 228 days · 100.0%
Health Impact Assessment
Excellent
Jo Daviess County's air quality is rated Excellent based on 94.3% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 94.3% 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 228 of 228 monitored days.
5-Year Air Quality Trend
Air quality is stable in Jo Daviess County. Best year: 2020 (337 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 337 | 16 | 0 | 0 | 32 | 87 |
| 2021 | 336 | 26 | 0 | 0 | 36 | 97 |
| 2022 | 328 | 15 | 0 | 0 | 34 | 84 |
| 2023 | 302 | 42 | 8 | 1 | 36 | 154 |
| 2024 | 327 | 21 | 1 | 0 | 36 | 101 |
| 2025 | 215 | 13 | 0 | 0 | 35 | 87 |
How does Jo Daviess County compare?
How Jo Daviess County compares
Good-day share better than US avg
Jo Daviess County 94.3%
Adams County, Illinois 94.4%
US average 76.5%
Median AQI better than US avg
Jo Daviess County 35
Adams County, Illinois 38
US average 38
Unhealthy days / yr about average
Jo Daviess 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 Jo Daviess 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 Jo Daviess 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 Jo Daviess County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Jo Daviess County with its Illinois neighbours before drawing a conclusion about the region. All of Illinois
Based on 228 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 Jo Daviess County, Illinois? ▼
Jo Daviess County has a median Air Quality Index (AQI) of 35, rated "Good." 94.3% of monitored days (215 out of 228) had good air quality in 2025.
What is the main pollutant in Jo Daviess County? ▼
The primary pollutant in Jo Daviess County is Ozone (O3), which was the main AQI driver on 228 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Jo Daviess County have? ▼
In 2025, Jo Daviess County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 87.
Is the air quality in Jo Daviess County getting better or worse? ▼
Air quality in Jo Daviess County is stable based on 5-year trends (2020-2025). Best year: 2020 with 337 good days. Worst year: 2025 with 215 good days.
What does AQI 35 mean for health? ▼
Jo Daviess 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 Jo Daviess County compare to other counties in Illinois? ▼
Jo Daviess County has 94.3% 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 Jo Daviess County? ▼
The 90th percentile AQI for Jo Daviess County is 47, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 87 (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.