Smoke: keep one room clean
Shut the windows and run an air purifier sized for the room.
Wildfire smoke guide →Air quality in Wisconsin, county by county
29 Wisconsin counties have enough EPA monitor data to count bad-air days. Weighted by population, they averaged about 7 days a year from 2021 to 2025 when the air was unhealthy for sensitive groups or worse.
CDC's model, which estimates every county from monitors and satellites, gives the average Wisconsin county, weighted by population, almost no smoky days (fine particles over 35.4 µg/m³, mostly wildfire smoke) and about 4 high-ozone days a year at its worst spot (2018 to 2022). See every county on the map.
Every Wisconsin county with monitors
Most bad-air days first. 21 have a full report. Compare with the worst and the cleanest counties in the US.
| County | Bad-air days a year | |
|---|---|---|
| Kenosha CountyKenoshaOzone | 14.2 | |
| Milwaukee CountyMilwaukeeOzone | 10.8 | |
| Ozaukee CountyMequonOzone | 10.8 | |
| Sheboygan CountySheboyganOzoneparticles not measured | 9.8 | |
| Racine CountyRacineOzoneparticles not measured | 9.5 | |
| Waukesha CountyWaukeshaOzone and particles | 8.2 | |
| Eau Claire CountyEau ClaireSummer smoke | 7.0 | |
| Dane CountyMadisonOzone and particles | 6.2 | |
| Forest CountySummer smoke | 6.2 | |
| Rock CountyJanesvilleOzoneparticles not measured | 6.0 | |
| Brown CountyGreen BaySummer smoke | 5.8 | |
| Sauk CountyBarabooOzone and particles | 5.4 | |
| Walworth CountyWhitewaterOzoneparticles not measured | 5.2 | |
| Dodge CountyBeaver DamOzone and particles | 5.2 | |
| Outagamie CountyAppletonSummer smoke | 5.2 | |
| Ashland CountySummer smoke | 4.8 | |
| Door CountyOzoneparticles not measured | 4.8 | |
| Kewaunee CountyOzoneparticles not measured | 4.7 | |
| Columbia CountyOzoneparticles not measured | 4.5 | |
| Jefferson CountyWatertownOzoneparticles not measured | 4.0 | |
| Manitowoc CountyManitowocOzoneparticles not measured | 4.0 | |
| Marathon CountyWausauOzone and particles | 3.8 | |
| Vilas CountySummer smoke | 3.8 | |
| Jackson CountySmokeozone not measured | 3.4 | |
| Taylor CountySummer smoke | 3.2 | |
| Monroe CountySpartaSmokeozone not measured | 3.0 | |
| La Crosse CountyLa CrosseSummer smoke | 2.8 | |
| Grant CountyPlattevilleSmokeozone not measured | 2.0 | |
| Fond du Lac CountyFond du LacOzoneparticles not measured | 1.2 | |
| No Wisconsin county with a monitor matches “”. Counties without a monitor aren't listed; a neighbor's numbers are a fair guide, or find it on the map. | ||
Counties without a monitor aren't listed. Air doesn't stop at the county line, so a neighbor's numbers are a fair guide.
What helps on a bad-air day
Check AirNow for today's reading and tomorrow's forecast, then match the step to the pollutant.
Upgrade the furnace filter
MERV 13 catches far more smoke than thin fiberglass filters.
Furnace filters →Questions people ask about air quality in Wisconsin
Which county in Wisconsin has the worst air?
Among Wisconsin counties with EPA monitors, Kenosha County had the most bad-air days from 2021 to 2025: about 14 bad-air days a year with an AQI over 100. That's about 1 day in 26.
How often is the air bad in Wisconsin?
Weighted by population, Wisconsin counties with monitors averaged about 7 bad-air days a year from 2021 to 2025 with an AQI over 100, when children, older adults and people with asthma should cut back outdoors. That's about 1 day in 49.
Which county in Wisconsin has the cleanest air?
Of the 29 counties with enough monitor data, Fond du Lac County had the fewest: 1.2 a year from 2021 to 2025. Counties without monitors aren't ranked.
Where can I check today's air quality in Wisconsin?
AirNow, run by the EPA and its partners, shows current readings and forecasts by ZIP code, and its fire and smoke map adds smoke plumes and low-cost sensors.
Sources: EPA AirData county AQI summaries, 2021 to 2025; CDC Environmental Public Health Tracking Network modeled PM2.5 and ozone, 2018 to 2022. Updated November 8, 2026.