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Air quality in Idaho

EPA monitors report from 20 of Idaho’s 44 counties. That is the honest limit of this page: the other 24 are not measured, not clean. In 2025 the most affected monitored county was Idaho County, with 8 days above the moderate category.

20
Counties with monitors
24
Counties without
27
Days above moderate, 2025
Summed across monitored counties
10.7%
Adults with asthma
Population-weighted county estimate

County by county

Monitored Idaho counties

GoodModerateUnhealthy for sensitive groupsUnhealthyVery unhealthyHazardous
County90th %ile AQIAbove moderateMax AQI2025 days by category
Idaho County628215
Bonner County664138
Nez Perce County634161
Kootenai County583118
Lemhi County632163
Bannock County521111
Boise County581135
Latah County571107
Shoshone County661111
Twin Falls County471105
Valley County601104
Ada County61097
Benewah County66092
Blaine County36075
Bonneville County43095
Boundary County55093
Butte County50077
Canyon County58091
Custer County31056
Franklin County39082

EPA Air Quality System annual summaries by county, 2025. The 90th percentile AQI describes a day worse than nine out of ten, which is a steadier measure than the annual maximum a single wildfire can set.

Not measured

24 counties without a monitor

No EPA monitor reported from these counties, so there is no air quality record to publish. Their radon zone is known, and radon is measured in the building rather than the air outside it.

Other states

Air quality elsewhere