Smoke: keep one room clean
Shut the windows and run an air purifier sized for the room.
Wildfire smoke guide →Air quality in Ohio, county by county
36 Ohio 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 Ohio county, weighted by population, almost no smoky days (fine particles over 35.4 µg/m³, mostly wildfire smoke) and about 3 high-ozone days a year at its worst spot (2018 to 2022). See every county on the map.
Every Ohio county with monitors
Most bad-air days first. 27 have a full report. Compare with the worst and the cleanest counties in the US.
| County | Bad-air days a year | |
|---|---|---|
| Hamilton CountyCincinnatiOzone | 10.4 | |
| Lucas CountyToledoOzone | 7.6 | |
| Cuyahoga CountyClevelandOzone | 7.0 | |
| Butler CountyHamiltonOzone | 6.6 | |
| Lake CountyMentorOzone | 6.0 | |
| Warren CountyMasonOzone | 5.0 | |
| Franklin CountyColumbusOzone and particles | 4.4 | |
| Montgomery CountyDaytonOzone | 4.4 | |
| Summit CountyAkronOzone and particles | 3.6 | |
| Trumbull CountyWarrenOzone and particles | 3.6 | |
| Stark CountyCantonOzone | 3.4 | |
| Ashtabula CountyAshtabulaOzoneparticles not measured | 2.8 | |
| Clark CountySpringfieldOzone | 2.8 | |
| Medina CountyBrunswickOzone and particles | 2.8 | |
| Preble CountyOzone and particles | 2.6 | |
| Clermont CountyOzone | 2.4 | |
| Clinton CountyWilmingtonOzoneparticles not measured | 2.4 | |
| Mahoning CountyYoungstownSummer smoke | 2.4 | |
| Portage CountyKentOzone | 2.4 | |
| Allen CountyLimaOzone | 1.8 | |
| Scioto CountyPortsmouthSmokeozone not measured | 1.8 | |
| Greene CountyBeavercreekOzoneparticles not measured | 1.6 | |
| Jefferson CountySteubenvilleSummer smoke | 1.6 | |
| Madison CountyLondonOzoneparticles not measured | 1.4 | |
| Miami CountyTroyOzoneparticles not measured | 1.4 | |
| Lawrence CountyIrontonSummer smoke | 1.2 | |
| Wood CountyBowling GreenOzoneparticles not measured | 1.2 | |
| Delaware CountyDelawareOzoneparticles not measured | 1.0 | |
| Geauga CountyOzoneparticles not measured | 1.0 | |
| Knox CountyMount VernonOzoneparticles not measured | 1.0 | |
| Licking CountyNewarkOzoneparticles not measured | 0.6 | |
| Noble CountyOzone | 0.6 | |
| Lorain CountyLorainRarely bad | 0.4 | |
| Washington CountyMariettaRarely badparticles not measured | 0.4 | |
| Athens CountyAthensRarely badozone not measured | 0.3 | |
| Belmont CountyRarely badozone not measured | 0.2 | |
| No Ohio 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 Ohio
Which county in Ohio has the worst air?
Among Ohio counties with EPA monitors, Hamilton 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 35.
How often is the air bad in Ohio?
Weighted by population, Ohio 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 79.
Which county in Ohio has the cleanest air?
Of the 36 counties with enough monitor data, Belmont County had the fewest: 0.2 a year from 2021 to 2025. Counties without monitors aren't ranked.
Where can I check today's air quality in Ohio?
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.