Median AQI
44
Good
Wisconsin · County air quality · 2025
Walworth County, Wisconsin
Median AQI 44 (Good). 75.0% of monitored days rated Good, direct from EPA Air Quality System stations.
- 44
- Median AQI
- 75.0%
- Good-air days
- 0
- Unhealthy days
- 41%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Walworth County's air is good on balance, more polluted than the median US county, a median AQI of 44 with 75.0% of 92 monitored days in the Good band, driven mainly by Ozone.
- 44
- median AQI · Good
- 75.0%
- days rated Good
- Ozone
- main pollutant
- 41%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 112.
Data updated July 2026
- Good · 69 d · 75.0%
- Moderate · 21 d · 22.8%
- USG · 2 d · 2.2%
How did Walworth County's air break down in 2025?
Across 92 monitored days, 69 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 112 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 92 days monitored. Median AQI: 44 (Good).
Insights: Walworth County, Wisconsin. EPA monitors recorded a median Air Quality Index of 44 across 92 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 69 (75%) fell in the Good band (AQI 0–50), 21 (23%) registered Moderate readings, and 2 (2%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 67, while the worst single-day peak hit 112 (USG). Residents averaged about 22.5 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (92 days). Across the 2020–2025 trend window, good days shifted by -111 and the median AQI moved +5 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 112, usg but never Unhealthy. Nearby counties show comparable readings: Ashland (85.6% good, AQI 39); Brown (79.0% good, AQI 37); Columbia (84.6% good, AQI 42); Dane (71.8% good, AQI 40); Dodge (76.4% good, AQI 39); Door (85.7% good, AQI 40).
Air Quality Summary
Good Days
75.0%
69 of 92 monitored days
0.0pp vs 75% target
Max AQI Recorded
112
USG
Health Grade
Good
90th-pct AQI 67
Walworth County, Good days share 75.0%
National avg
Share of monitored days at AQI 0-50 (Good band).
Walworth 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 92 monitored days across EPA AQI categories.
Good
69
75%
Moderate
21
23%
USG
2
2%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Walworth County.
- Ozone · 92 days · 100.0%
Health Impact Assessment
Good
Walworth County's air quality is rated Good based on 75.0% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 75.0% of monitored days in 2025, with a median AQI of 44. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 92 of 92 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Walworth County. Best year: 2021 (184 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 180 | 14 | 4 | 0 | 39 | 136 |
| 2021 | 184 | 36 | 1 | 0 | 41 | 101 |
| 2022 | 181 | 16 | 3 | 0 | 39 | 105 |
| 2023 | 138 | 48 | 17 | 0 | 44 | 143 |
| 2024 | 169 | 37 | 0 | 0 | 42 | 100 |
| 2025 | 69 | 21 | 2 | 0 | 44 | 112 |
How does Walworth County compare?
How Walworth County compares
Good-day share worse than US avg
Walworth County 75.0%
Ashland County, Wisconsin 85.6%
US average 76.5%
Median AQI worse than US avg
Walworth County 44
Ashland County, Wisconsin 39
US average 38
Unhealthy days / yr about average
Walworth County 0
Ashland County, Wisconsin 1
US average 0
Other Counties in Wisconsin
Air quality comparison for nearby counties in Wisconsin.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Walworth County.
Baltimore County, Maryland
AQI 44 · 70.4% good
Baltimore (City) County, Maryland
AQI 44 · 68.7% good
Bartholomew County, Indiana
AQI 44 · 69.2% good
Berks County, Pennsylvania
AQI 44 · 65.6% good
Bolivar County, Mississippi
AQI 44 · 70.3% good
Brewster County, Texas
AQI 44 · 69.0% good
What Walworth 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 44 means for exposure. Health guidance
- See how Walworth County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Walworth County with its Wisconsin neighbours before drawing a conclusion about the region. All of Wisconsin
Based on 92 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 Walworth County, Wisconsin? ▼
Walworth County has a median Air Quality Index (AQI) of 44, rated "Good." 75.0% of monitored days (69 out of 92) had good air quality in 2025.
What is the main pollutant in Walworth County? ▼
The primary pollutant in Walworth County is Ozone (O3), which was the main AQI driver on 92 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Walworth County have? ▼
In 2025, Walworth County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 112.
Is the air quality in Walworth County getting better or worse? ▼
Air quality in Walworth County is worsening based on 5-year trends (2020-2025). Best year: 2021 with 184 good days. Worst year: 2025 with 69 good days.
What does AQI 44 mean for health? ▼
Walworth County's median AQI of 44 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 Walworth County compare to other counties in Wisconsin? ▼
Walworth County has 75.0% good air days. Nearby counties in Wisconsin: Ashland (85.6% good), Brown (79.0% good), Columbia (84.6% good), Dane (71.8% good), Dodge (76.4% good), Door (85.7% good).
What is the 90th percentile AQI in Walworth County? ▼
The 90th percentile AQI for Walworth County is 67, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 112 (USG).
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.