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Air quality in Indiana

EPA monitors report from 33 of Indiana’s 92 counties. That is the honest limit of this page: the other 59 are not measured, not clean. In 2025 the most affected monitored county was Lake County, with 15 days above the moderate category.

33
Counties with monitors
59
Counties without
89
Days above moderate, 2025
Summed across monitored counties
11.2%
Adults with asthma
Population-weighted county estimate

County by county

Monitored Indiana counties

GoodModerateUnhealthy for sensitive groupsUnhealthyVery unhealthyHazardous
County90th %ile AQIAbove moderateMax AQI2025 days by category
Lake County7515219
LaPorte County7212153
Porter County7111136
St. Joseph County717127
Elkhart County666171
Floyd County615126
Hamilton County625118
Marion County715170
Allen County693115
Boone County513112
Clark County613133
Howard County613122
Delaware County632108
Madison County612122
Whitley County612108
Carroll County491105
Posey County501105
Shelby County491105
Vigo County651108
Wabash County491112
Bartholomew County59097
Brown County46077
Dubois County58088
Greene County59090
Hendricks County49090
Henry County59095
Knox County49093
Monroe County58084
Perry County49084
Spencer County59088
Tippecanoe County58095
Vanderburgh County630100
Warrick County54097

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

59 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