Median AQI
37
Good
Indiana · County air quality · 2025
Carroll County, Indiana
Median AQI 37 (Good). 87.8% of monitored days rated Good, direct from EPA Air Quality System stations.
- 37
- Median AQI
- 87.8%
- Good-air days
- 0
- Unhealthy days
- 71%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Carroll County's air is good on balance, cleaner than the median US county, a median AQI of 37 with 87.8% of 255 monitored days in the Good band, driven mainly by Ozone.
- 37
- median AQI · Good
- 87.8%
- days rated Good
- Ozone
- main pollutant
- 71%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 105.
Data updated July 2026
- Good · 224 d · 87.8%
- Moderate · 30 d · 11.8%
- USG · 1 d · 0.4%
How did Carroll County's air break down in 2025?
Across 255 monitored days, 224 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 105 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 255 days monitored. Median AQI: 37 (Good).
Insights: Carroll County, Indiana. EPA monitors recorded a median Air Quality Index of 37 across 255 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 224 (88%) fell in the Good band (AQI 0–50), 30 (12%) registered Moderate readings, and 1 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 54, while the worst single-day peak hit 105 (USG). Residents averaged about 26.4 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (255 days). Across the 2020–2025 trend window, good days shifted by -128 and the median AQI moved +6 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 105, usg but never Unhealthy. Nearby counties show comparable readings: Allen (58.2% good, AQI 45); Bartholomew (69.2% good, AQI 44); Boone (86.9% good, AQI 38); Brown (94.5% good, AQI 37); Clark (59.7% good, AQI 46); Delaware (63.4% good, AQI 44).
Air Quality Summary
Good Days
87.8%
224 of 255 monitored days
12.8pp vs 75% target
Max AQI Recorded
105
USG
Health Grade
Good
90th-pct AQI 54
Carroll County, Good days share 87.8%
National avg
Share of monitored days at AQI 0-50 (Good band).
Carroll County, Unhealthy-or-worse share 0.0%
National avg
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
AQI Day Breakdown (2025)
Distribution of 255 monitored days across EPA AQI categories.
Good
224
88%
Moderate
30
12%
USG
1
0%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Carroll County.
- Ozone · 255 days · 100.0%
Health Impact Assessment
Good
Carroll County's air quality is rated Good based on 87.8% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 87.8% of monitored days in 2025, with a median AQI of 37. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 255 of 255 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Carroll County. Best year: 2020 (352 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 352 | 12 | 0 | 0 | 31 | 100 |
| 2021 | 338 | 26 | 1 | 0 | 34 | 105 |
| 2022 | 343 | 21 | 0 | 0 | 34 | 93 |
| 2023 | 308 | 38 | 5 | 0 | 36 | 122 |
| 2024 | 317 | 44 | 0 | 0 | 36 | 90 |
| 2025 | 224 | 30 | 1 | 0 | 37 | 105 |
How does Carroll County compare?
How Carroll County compares
Good-day share better than US avg
Carroll County 87.8%
Allen County, Indiana 58.2%
US average 76.5%
Median AQI better than US avg
Carroll County 37
Allen County, Indiana 45
US average 38
Unhealthy days / yr about average
Carroll County 0
Allen County, Indiana 0
US average 0
Other Counties in Indiana
Air quality comparison for nearby counties in Indiana.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Carroll County.
Alachua County, Florida
AQI 37 · 90.1% good
Beltrami County, Minnesota
AQI 37 · 88.8% good
Benewah County, Idaho
AQI 37 · 74.6% good
Brevard County, Florida
AQI 37 · 89.7% good
Brown County, Indiana
AQI 37 · 94.5% good
Brown County, Wisconsin
AQI 37 · 79.0% good
What Carroll County's air means for you
The air here stays in the breathable range year-round, with Ozone the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 37 means for exposure. Health guidance
- See how Carroll County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Carroll County with its Indiana neighbours before drawing a conclusion about the region. All of Indiana
Based on 255 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
More Air Quality Data
Air Quality Guides
Frequently Asked Questions
What is the air quality in Carroll County, Indiana? ▼
Carroll County has a median Air Quality Index (AQI) of 37, rated "Good." 87.8% of monitored days (224 out of 255) had good air quality in 2025.
What is the main pollutant in Carroll County? ▼
The primary pollutant in Carroll County is Ozone (O3), which was the main AQI driver on 255 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Carroll County have? ▼
In 2025, Carroll County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 105.
Is the air quality in Carroll County getting better or worse? ▼
Air quality in Carroll County is worsening based on 5-year trends (2020-2025). Best year: 2020 with 352 good days. Worst year: 2025 with 224 good days.
What does AQI 37 mean for health? ▼
Carroll County's median AQI of 37 falls in the "Good" category. See the <a href="/guides/understanding-aqi" class="underline">AQI category guide</a> for what each range means for health.
How does Carroll County compare to other counties in Indiana? ▼
Carroll County has 87.8% good air days. Nearby counties in Indiana: Allen (58.2% good), Bartholomew (69.2% good), Boone (86.9% good), Brown (94.5% good), Clark (59.7% good), Delaware (63.4% good).
What is the 90th percentile AQI in Carroll County? ▼
The 90th percentile AQI for Carroll County is 54, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 105 (USG).
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025 (aqs.epa.gov). For current conditions (not shown here — this page is historical annual data), see EPA AirNow (airnow.gov). See our methodology for how AQI, median, and coverage figures are computed.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer.
Every figure on PlainAir 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.