Which county in Indiana has the best air quality?

Based on 2024 EPA AQS data, Spencer County had the best air quality in Indiana with a median AQI of 34 and 132 good-air days.

2024 monitoring year Public dataset EPA AQS

Indiana Air Quality Rankings

Compiled by PlainEnviro Editorial, Environmental Data Editorial Team · July 13, 2026

County-level AQI rollup using EPA Air Quality System monitor records. Refreshed as new EPA AQS data lands.

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County-by-county air quality data for Indiana based on EPA AQS annual AQI readings. Data covers 34 monitored counties for 2024.

Indiana (2024): 34 counties monitored. State average median AQI: 41 (national average: 38.8). 74% of monitored days rated "Good." Most unhealthy air: Floyd County (1 days above AQI 100).

Indiana air quality on this page is drawn from the EPA Air Quality System (AQS), which aggregates daily readings from federal, state, tribal, and local monitors into annual summaries per county. The current dataset covers 34 Indiana counties with at least ten days of valid AQI readings in 2024, out of the state's total monitored counties.

The state-average median AQI across those counties is 41, compared with a national average of 38.8 in the same reporting period. On average, 74% of monitored days fell into the "Good" AQI bucket (0–50). The heaviest burden of unhealthy days lands on Floyd County (1 day above AQI 100), while Spencer County records the cleanest air with a median AQI of 34.

AQI values translate ambient concentrations of pollutants (ozone, PM2.5, PM10, NO₂, SO₂, CO) onto a single 0–500 scale with six health-based bands. A low median AQI reflects typical daily conditions; peak values matter separately because short-term exposure drives most acute health effects. Counties without monitors are not "clean" - they are simply unmeasured by EPA AQS. For site-specific exposure guidance, check AirNow.gov alongside the county detail links below.

Counties with Data

State Avg Median AQI

National Avg Median AQI

38.8

Avg Good Days %

74%

Which Indiana counties have the worst air quality?

Ranked by median AQI (higher = worse). Click a county for full environmental data.

#	County	Median AQI	Good Days	Good %	Unhealthy Days	Peak AQI
1	Marion	54	134	37%	0	138
2	Lake	52	162	44%	1	166
3	Clark	47	216	59%	0	150
4	Vigo	47	204	56%	0	112
5	Vanderburgh	46	227	62%	0	119
6	Elkhart	45	227	62%	0	145
7	St Joseph	45	237	65%	0	119
8	Allen	45	229	63%	0	100
9	Hamilton	44	244	67%	0	108
10	Bartholomew	44	262	72%	0	101
11	Delaware	44	240	66%	0	97
12	Porter	44	243	66%	0	112
13	Howard	44	241	66%	0	93
14	Floyd	43	257	71%	1	154
15	Madison	42	263	72%	0	97
16	Greene	42	266	73%	0	97
17	Laporte	41	257	70%	0	115
18	Dubois	39	265	72%	0	70
19	Perry	39	286	87%	0	90
20	Sullivan	39	23	74%	0	59
21	Knox	38	314	87%	0	90
22	Warrick	38	326	89%	0	101
23	Posey	37	340	93%	0	122
24	Brown	37	339	94%	0	77
25	Boone	36	313	87%	0	93
26	Shelby	36	331	91%	0	87
27	Carroll	36	317	88%	0	90
28	Wabash	36	324	89%	0	84
29	Hendricks	35	331	94%	0	80
30	Whitley	35	278	76%	0	70
31	Tippecanoe	35	256	74%	0	67
32	Henry	34	282	78%	0	75
33	Monroe	34	290	81%	0	63
34	Spencer	34	132	78%	0	68

Frequently Asked Questions

What is the air quality like in Indiana?

In 2024, Indiana had an average median AQI of 41 across 34 monitored counties, with 74% of monitored days rated "Good" (AQI 0–50). The national average median AQI is 38.8.

Which county in Indiana has the worst air quality?

Based on 2024 EPA AQS data, Floyd County had the most unhealthy air days in Indiana - 1 days above AQI 100, with a median AQI of 43.

Explore More

National AQI Rankings → Indiana Full Profile → Indiana Water Quality →

About This Data

Air quality data is from the EPA Air Quality System (AQS), Annual AQI by County dataset. Counties with fewer than 10 monitored days are excluded. "Unhealthy days" counts days with AQI above 100 (Unhealthy for Sensitive Groups or worse). All data is for 2024.

Source: U.S. Environmental Protection Agency, Air Quality System (AQS) U.S. Environmental Protection Agency, Air Quality System (AQS)

Read our methodology - how this data is sourced, computed, and verified.

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Data sourced from the U.S. Environmental Protection Agency (EPA). See our methodology for details. Retrieved and formatted by PlainEnviro Editorial