Median AQI
44
Good
Kentucky · County air quality · 2025
Hardin County, Kentucky
Median AQI 44 (Good). 72.4% of monitored days rated Good, direct from EPA Air Quality System stations.
- 44
- Median AQI
- 72.4%
- Good-air days
- 0
- Unhealthy days
- 36%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Hardin County's air is good on balance, more polluted than the median US county, a median AQI of 44 with 72.4% of 127 monitored days in the Good band, driven mainly by Ozone.
- 44
- median AQI · Good
- 72.4%
- days rated Good
- Ozone
- main pollutant
- 36%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 73.
Data updated July 2026
- Good · 92 d · 72.4%
- Moderate · 35 d · 27.6%
How did Hardin County's air break down in 2025?
Across 127 monitored days, 92 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 73 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 127 days monitored. Median AQI: 44 (Good).
Insights: Hardin County, Kentucky. EPA monitors recorded a median Air Quality Index of 44 across 127 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 92 (72%) fell in the Good band (AQI 0–50), 35 (28%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 56, while the worst single-day peak hit 73 (Moderate). Residents averaged about 21.7 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (75 days), PM2.5 (52 days). Across the 2020–2025 trend window, good days shifted by -176 and the median AQI moved +1 points, placing the multi-year trajectory at stable. The worst single reading over the 2020–2025 window was AQI 73, moderate but never Unhealthy. Nearby counties show comparable readings: Bell (63.5% good, AQI 43); Boone (95.1% good, AQI 38); Boyd (82.8% good, AQI 39); Bullitt (92.7% good, AQI 39); Campbell (78.5% good, AQI 39); Carter (89.8% good, AQI 36).
Air Quality Summary
Good Days
72.4%
92 of 127 monitored days
-2.6pp vs 75% target
Max AQI Recorded
73
Moderate
Health Grade
Moderate
90th-pct AQI 56
Hardin County, Good days share 72.4%
National avg
Share of monitored days at AQI 0-50 (Good band).
Hardin 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 127 monitored days across EPA AQI categories.
Good
92
72%
Moderate
35
28%
USG
0
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 Hardin County.
- Ozone · 75 days · 59.1%
- PM2.5 · 52 days · 40.9%
Health Impact Assessment
Moderate
Hardin County's air quality is rated Moderate based on 72.4% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 72.4% of monitored days in 2025, with a median AQI of 44. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 75 of 127 monitored days.
5-Year Air Quality Trend
Air quality is stable in Hardin County. Best year: 2020 (268 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 268 | 98 | 0 | 0 | 43 | 80 |
| 2021 | 238 | 125 | 1 | 0 | 43 | 101 |
| 2022 | 242 | 120 | 0 | 0 | 44 | 86 |
| 2023 | 225 | 136 | 3 | 1 | 45 | 151 |
| 2024 | 129 | 25 | 0 | 0 | 41 | 67 |
| 2025 | 92 | 35 | 0 | 0 | 44 | 73 |
How does Hardin County compare?
How Hardin County compares
Good-day share worse than US avg
Hardin County 72.4%
Bell County, Kentucky 63.5%
US average 76.5%
Median AQI worse than US avg
Hardin County 44
Bell County, Kentucky 43
US average 38
Unhealthy days / yr about average
Hardin County 0
Bell County, Kentucky 0
US average 0
Other Counties in Kentucky
Air quality comparison for nearby counties in Kentucky.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Hardin County.
Baltimore County, Maryland
AQI 44 · 70.4% good
Baltimore (City) County, Maryland
AQI 44 · 68.7% good
Bartholomew County, Indiana
AQI 44 · 69.2% good
Berks County, Pennsylvania
AQI 44 · 65.6% good
Bolivar County, Mississippi
AQI 44 · 70.3% good
Brewster County, Texas
AQI 44 · 69.0% good
What Hardin 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 44 means for exposure. Health guidance
- See how Hardin County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Hardin County with its Kentucky neighbours before drawing a conclusion about the region. All of Kentucky
Based on 127 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 Hardin County, Kentucky? ▼
Hardin County has a median Air Quality Index (AQI) of 44, rated "Good." 72.4% of monitored days (92 out of 127) had good air quality in 2025.
What is the main pollutant in Hardin County? ▼
The primary pollutant in Hardin County is Ozone (O3), which was the main AQI driver on 75 days (59% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Hardin County have? ▼
In 2025, Hardin County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 73.
Is the air quality in Hardin County getting better or worse? ▼
Air quality in Hardin County is stable based on 5-year trends (2020-2025). Best year: 2020 with 268 good days. Worst year: 2025 with 92 good days.
What does AQI 44 mean for health? ▼
Hardin County's median AQI of 44 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 Hardin County compare to other counties in Kentucky? ▼
Hardin County has 72.4% good air days. Nearby counties in Kentucky: Bell (63.5% good), Boone (95.1% good), Boyd (82.8% good), Bullitt (92.7% good), Campbell (78.5% good), Carter (89.8% good).
What is the 90th percentile AQI in Hardin County? ▼
The 90th percentile AQI for Hardin County is 56, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 73 (Moderate).
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.