Median AQI
39
Good
Wisconsin · County air quality · 2025
Fond du Lac County, Wisconsin
Median AQI 39 (Good). 91.3% of monitored days rated Good, direct from EPA Air Quality System stations.
- 39
- Median AQI
- 91.3%
- Good-air days
- 0
- Unhealthy days
- 79%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Fond du Lac County's air is good on balance, cleaner than most US counties, a median AQI of 39 with 91.3% of 92 monitored days in the Good band, driven mainly by Ozone.
- 39
- median AQI · Good
- 91.3%
- days rated Good
- Ozone
- main pollutant
- 79%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 80.
Data updated July 2026
- Good · 84 d · 91.3%
- Moderate · 8 d · 8.7%
How did Fond du Lac County's air break down in 2025?
Across 92 monitored days, 84 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 80 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 92 days monitored. Median AQI: 39 (Good).
Insights: Fond du Lac County, Wisconsin. EPA monitors recorded a median Air Quality Index of 39 across 92 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 84 (91%) fell in the Good band (AQI 0–50), 8 (9%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 50, while the worst single-day peak hit 80 (Moderate). Residents averaged about 27.4 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 -110 and the median AQI moved +3 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 80, moderate 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
91.3%
84 of 92 monitored days
16.3pp vs 75% target
Max AQI Recorded
80
Moderate
Health Grade
Excellent
90th-pct AQI 50
Fond du Lac County, Good days share 91.3%
National avg
Share of monitored days at AQI 0-50 (Good band).
Fond du Lac 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
84
91%
Moderate
8
9%
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 Fond du Lac County.
- Ozone · 92 days · 100.0%
Health Impact Assessment
Excellent
Fond du Lac County's air quality is rated Excellent based on 91.3% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 91.3% of monitored days in 2025, with a median AQI of 39. 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 Fond du Lac County. Best year: 2020 (194 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 194 | 9 | 2 | 0 | 36 | 115 |
| 2021 | 178 | 30 | 0 | 0 | 39 | 90 |
| 2022 | 193 | 9 | 1 | 0 | 36 | 108 |
| 2023 | 162 | 38 | 4 | 0 | 41 | 122 |
| 2024 | 190 | 15 | 0 | 0 | 38 | 77 |
| 2025 | 84 | 8 | 0 | 0 | 39 | 80 |
How does Fond du Lac County compare?
How Fond du Lac County compares
Good-day share better than US avg
Fond du Lac County 91.3%
Ashland County, Wisconsin 85.6%
US average 76.5%
Median AQI worse than US avg
Fond du Lac County 39
Ashland County, Wisconsin 39
US average 38
Unhealthy days / yr about average
Fond du Lac 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 Fond du Lac County.
Ada County, Idaho
AQI 39 · 80.6% good
Aiken County, South Carolina
AQI 39 · 89.1% good
Albany County, New York
AQI 39 · 67.4% good
Alexander County, North Carolina
AQI 39 · 92.4% good
Ashland County, Wisconsin
AQI 39 · 85.6% good
Bennington County, Vermont
AQI 39 · 82.9% good
What Fond du Lac 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 39 means for exposure. Health guidance
- See how Fond du Lac County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Fond du Lac 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 Fond du Lac County, Wisconsin? ▼
Fond du Lac County has a median Air Quality Index (AQI) of 39, rated "Good." 91.3% of monitored days (84 out of 92) had good air quality in 2025.
What is the main pollutant in Fond du Lac County? ▼
The primary pollutant in Fond du Lac 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 Fond du Lac County have? ▼
In 2025, Fond du Lac County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 80.
Is the air quality in Fond du Lac County getting better or worse? ▼
Air quality in Fond du Lac County is worsening based on 5-year trends (2020-2025). Best year: 2020 with 194 good days. Worst year: 2025 with 84 good days.
What does AQI 39 mean for health? ▼
Fond du Lac County's median AQI of 39 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 Fond du Lac County compare to other counties in Wisconsin? ▼
Fond du Lac County has 91.3% 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 Fond du Lac County? ▼
The 90th percentile AQI for Fond du Lac County is 50, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 80 (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.