Smoke: keep one room clean
Shut the windows and run an air purifier sized for the room.
Wildfire smoke guide →Air quality in Indiana, county by county
32 Indiana counties have enough EPA monitor data to count bad-air days. Weighted by population, they averaged about 5 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 Indiana county, weighted by population, almost no smoky days (fine particles over 35.4 µg/m³, mostly wildfire smoke) and about 2 high-ozone days a year at its worst spot (2018 to 2022). See every county on the map.
Every Indiana county with monitors
Most bad-air days first. 20 have a full report. Compare with the worst and the cleanest counties in the US.
| County | Bad-air days a year | |
|---|---|---|
| Lake CountyHammondOzone | 9.8 | |
| Marion CountyOzone and particles | 9.8 | |
| Porter CountyPortageOzone | 9.6 | |
| LaPorte CountyMichigan CityOzone | 6.8 | |
| St. Joseph CountySouth BendOzone | 5.8 | |
| Howard CountyKokomoOzone | 4.2 | |
| Clark CountyJeffersonvilleOzone | 3.8 | |
| Madison CountyAndersonOzone | 3.6 | |
| Elkhart CountyElkhartOzone and particles | 3.4 | |
| Henry CountyNew CastleSmokeozone not measured | 3.3 | |
| Hamilton CountyFishersOzone | 3.2 | |
| Boone CountyZionsvilleOzoneparticles not measured | 2.8 | |
| Floyd CountyNew AlbanyOzone | 2.6 | |
| Greene CountyOzone | 2.6 | |
| Vigo CountyTerre HauteOzone | 2.4 | |
| Vanderburgh CountyEvansvilleOzone | 2.2 | |
| Allen CountyFort WayneOzone | 2.0 | |
| Bartholomew CountyColumbusOzone | 2.0 | |
| Knox CountyVincennesOzoneparticles not measured | 2.0 | |
| Warrick CountyOzoneparticles not measured | 2.0 | |
| Whitley CountyColumbia CitySmokeozone not measured | 2.0 | |
| Posey CountyOzoneparticles not measured | 1.8 | |
| Delaware CountyMuncieOzone | 1.6 | |
| Carroll CountyOzoneparticles not measured | 1.4 | |
| Shelby CountyShelbyvilleOzoneparticles not measured | 1.4 | |
| Tippecanoe CountyLafayetteSmokeozone not measured | 1.2 | |
| Wabash CountyWabashOzoneparticles not measured | 1.2 | |
| Monroe CountyBloomingtonSmokeozone not measured | 1.0 | |
| Hendricks CountyPlainfieldOzoneparticles not measured | 0.8 | |
| Perry CountyOzoneparticles not measured | 0.6 | |
| Brown CountyRarely badparticles not measured | 0.4 | |
| Dubois CountyJasperRarely badozone not measured | 0.3 | |
| No Indiana 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 Indiana
Which county in Indiana has the worst air?
Among Indiana counties with EPA monitors, Lake County had the most bad-air days from 2021 to 2025: about 10 bad-air days a year with an AQI over 100. That's about 1 day in 37.
How often is the air bad in Indiana?
Weighted by population, Indiana counties with monitors averaged about 5 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 71.
Which county in Indiana has the cleanest air?
Of the 32 counties with enough monitor data, Dubois County had the fewest: 0.3 a year from 2021 to 2025. Counties without monitors aren't ranked.
Where can I check today's air quality in Indiana?
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.