State air quality · 2025

Indiana Air Quality Ranking

Across 33 monitored counties, the typical county in Indiana posts a median AQI of 41 (Good) and 71.8% of monitored days were rated Good, from EPA AQS.

41
Avg median AQI
71.8%
Good-air days
33
Counties monitored
27%
Cleaner than US states

Indiana's typical county median AQI is 41 (Good) across 33 monitored counties

According to the U.S. EPA Air Quality System, Indiana monitors 33 counties with a day-weighted Good-day share of 71.8%. Cleanest: Brown County (95.9% Good). Most polluted: Marion County (40.0%). These are annual summaries, not live AirNow readings.

Data source EPA Air Quality System (AQS)

Cleaner than US states
Indiana's day-weighted Good-day share of 71.8% places it cleaner than 27% of US states.
In-state spread
Within Indiana, Brown County leads at 95.9% Good days while Marion County sits at 40.0% across 33 monitored counties.
2024→2025 release
Indiana's Good-day share moved -1.6 points vs the 2024 EPA annual release.
Typical median AQI
Typical median AQI: 41

Verify with AirNow → · EPA AQS →

EPA state monitoring brief

AQS state key INDIANA

Indiana · 2025 EPA AQS · 33 counties · med AQI 41 · 71.8% Good · Brown→Marion spread

  • GOOD 41 Median AQI · Good
  • SHARE 71.8% Good-day share
  • COUNT 33 Counties monitored
  • UNH 8 Unhealthy+ days
  • RANK 27% Cleaner than states
  • O3 52.7% Main pollutant share

Good-day share peers

Indiana (this)71.8%Colorado71.7%South Carolina71.3%Arkansas71.2%
Good-day share neighbourhood · nearest ABS peers vs Indiana

Indiana's 71.8% Good-day share is cleaner than 27% of monitored US states; Brown and Marion County bracket the in-state range. Open Brown County →

According to EPA AQS annual summaries on PlainAirData, Indiana ranks #38 of 52 by day-weighted good-day share (71.8%) and #35 by mean county median AQI (40.7). Hawaii is #1 of 52 by day-weighted good-day share (93.8% of monitored days) at mean county median-AQI #4 (27.3) ≠ Alaska #1 lowest mean county median AQI (20.3) at good-day share #8 (84.4%).

Data updated August 2026

What changed, what drives it, and how thick is the sample

Three derived views WPR-style word count does not substitute for: release-over-release movement from county annual rows, the EPA main-pollutant day mix, and how many counties sit below the 100-day ranking floor.

Release change

71.8%

Good-day share in 2025, down 1.6 percentage points vs 2024. County-mean median AQI 41, within half a point of the 2024 county-mean median.

Pollutant mix

Ozone

Main driver on 52.7% of pollutant-assigned days.

  • Ozone 52.7%
  • PM2.5 47.1%
  • PM10 0.1%

Monitoring coverage

359

Average monitored days per county in the latest release. Every monitored county clears the 100-day ranking floor.

Counties Monitored

33

Good Days %

71.8%

Avg Median AQI

41

Total Unhealthy Days

8

Best Air Quality

Brown County

Worst Air Quality

Marion County

Where Indiana sits nationally

COUNT-derived placement among 52 US states with at least 365 monitored days in the latest county release. Indiana's day-weighted Good-day share is 71.8% - cleaner than 27% of that comparison set.

Indiana Good-day share vs. every US state

Day-weighted share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release

71.8% 27th percentile higher than 27% of 52 US states

0.0%–5.0%: 0 US states (0%). Below this entry. 5.0%–10.0%: 0 US states (0%). Below this entry. 10.0%–15.0%: 0 US states (0%). Below this entry. 15.0%–20.0%: 0 US states (0%). Below this entry. 20.0%–25.0%: 0 US states (0%). Below this entry. 25.0%–30.0%: 0 US states (0%). Below this entry. 30.0%–35.0%: 0 US states (0%). Below this entry. 35.0%–40.0%: 0 US states (0%). Below this entry. 40.0%–45.0%: 0 US states (0%). Below this entry. 45.0%–50.0%: 0 US states (0%). Below this entry. 50.0%–55.0%: 0 US states (0%). Below this entry. 55.0%–60.0%: 0 US states (0%). Below this entry. 60.0%–65.0%: 2 US states (4%). Below this entry. 65.0%–70.0%: 9 US states (17%). Below this entry. 70.0%–75.0%: 11 US states (21%). This entry sits in this band. 75.0%–80.0%: 11 US states (21%). Above this entry. 80.0%–85.0%: 13 US states (25%). Above this entry. 85.0%–90.0%: 5 US states (10%). Above this entry. 90.0%–95.0%: 1 US states (2%). Above this entry. 95.0%–100.0%: 0 US states (0%). Above this entry. 100.0%–105.0%: 0 US states (0%). Above this entry. This state 0.0% 100% every floor-qualified US state, bucketed by value

Each bar is a band; taller bars hold more US states. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count, share, and where it sits relative to this entry.

Source U.S. Environmental Protection Agency, Air Quality System (AQS) · 2025

Which counties in Indiana have the cleanest and most polluted air?

Cleanest counties in Indiana

Share of monitored days rated Good (AQI 0–50)

  1. 1 Brown County 95.9%
  2. 2 Perry County 92.7%
  3. 3 Wabash County 92%
  4. 4 Hendricks County 92%
  5. 5 Shelby County 91.4%
  6. 6 Knox County 91.3%
  7. 7 Carroll County 90.8%
  8. 8 Posey County 90.5%
  9. 9 Boone County 89.7%
  10. 10 Warrick County 87.4%
  11. 11 Monroe County 73.6%
  12. 12 Bartholomew County 72.6%

Good-day share · EPA Air Quality System

County Good % Median AQI
Brown 95.9% 34
Perry 92.7% 36
Wabash 92.0% 34
Hendricks 92.0% 35
Shelby 91.4% 35
Knox 91.3% 36
Carroll 90.8% 35
Posey 90.5% 35
Boone 89.7% 35
Warrick 87.4% 37
Monroe 73.6% 36
Bartholomew 72.6% 43
Greene 72.0% 42
Madison 71.2% 41
Tippecanoe 70.3% 39
Henry 69.9% 37
Dubois 69.7% 39
Spencer 67.4% 39
Howard 66.6% 43
St. Joseph 66.0% 43
Floyd 65.8% 44
Delaware 64.7% 43
Whitley 64.2% 39
Hamilton 64.0% 44
LaPorte 63.0% 43
Porter 61.9% 44
Elkhart 61.0% 43
Allen 60.0% 44
Vigo 59.7% 45
Vanderburgh 59.5% 47
Clark 58.1% 46
Lake 41.6% 53
Marion 40.0% 54

Data Sources

Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025. See our methodology for how AQI and median figures are computed.

Coverage: 33 counties in Indiana with active monitoring stations. Unmonitored counties are not represented.

Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files, aggregated to the state level · 2020–2025

Every figure on PlainAirData is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.

Informational only, not professional advice. Data from EPA AQS. See our disclaimer.