Median AQI
39
Good
Kentucky · County air quality · 2025
Oldham County, Kentucky
Median AQI 39 (Good). 87.7% of monitored days rated Good, direct from EPA Air Quality System stations.
- 39
- Median AQI
- 87.7%
- Good-air days
- 0
- Unhealthy days
- 76%
- Cleaner than US counties
Oldham County's 2025 annual median AQI is 39 (Good), with 87.7% Good days
According to the U.S. EPA Air Quality System, Oldham County, Kentucky posted a 2025 median AQI of 39 (Good) across 244 monitored days, with 87.7% rated Good and 0 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Oldham County's 87.7% Good-day share places it cleaner than 76% of US counties in 2025.
- Closest median-AQI peer
- Aiken County (90.6% Good, median AQI 39) is the closest nationwide median-AQI peer to Oldham County.
- 2020–2025 trend
- Oldham County's floor-qualifying Good-day share is worsening from 2020 to 2025 (91.2% → 87.7%).
- Median AQI
- Median AQI: 39
The verdict
According to EPA Air Quality System monitoring data, Oldham County's air is good on balance, cleaner than most US counties, a median AQI of 39 with 87.7% of 244 monitored days in the Good band, driven mainly by Ozone.
- 39
- median AQI · Good
- 87.7%
- days rated Good
- Ozone
- main pollutant
- 76%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 108.
Annual release change
What changed in the 2025 EPA annual release
- Oldham County's Good-day share rose from 80.2% to 87.7% between the 2024 and 2025 EPA annual releases, a change of +7.5 percentage points.
- Oldham County's peak single-day AQI fell from 136 to 108 between the 2024 and 2025 EPA annual releases, a change of -28 points.
- Oldham County's median AQI fell from 43 to 39 between the 2024 and 2025 EPA annual releases, a change of -4 points.
Data updated August 2026
- Good · 214 d · 87.7%
- Moderate · 28 d · 11.5%
- USG · 2 d · 0.8%
How did Oldham County's air break down in 2025?
Across 244 monitored days, 214 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 108 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 244 days monitored. Median AQI: 39 (Good).
Insights: Oldham County, Kentucky. EPA monitors recorded a median Air Quality Index of 39 across 244 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 214 (88%) fell in the Good band (AQI 0–50), 28 (11%) registered Moderate readings, and 2 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 51, while the worst single-day peak hit 108 (USG). Residents averaged about 26.3 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (244 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by -3.5 points and the median AQI moved +1 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 108, usg but never Unhealthy. Nearby counties show comparable readings: Bell (67.0% good, AQI 42); Boone (87.6% good, AQI 38); Boyd (80.0% good, AQI 39); Bullitt (88.4% good, AQI 39); Campbell (75.6% good, AQI 39); Carter (89.0% good, AQI 36).
Air Quality Summary
Good Days
87.7%
214 of 244 monitored days
12.7pp vs 75% target
Max AQI Recorded
108
USG
Health Grade
Good
90th-pct AQI 51
Oldham County, Good days share 87.7%
National avg
Share of monitored days at AQI 0-50 (Good band).
Oldham 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 244 monitored days across EPA AQI categories.
Good
214
88%
Moderate
28
11%
USG
2
1%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Oldham County.
- Ozone · 244 days · 100.0%
Health Impact Assessment
Good
Oldham County's air quality is rated Good based on 87.7% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 87.7% of monitored days in 2025, with a median AQI of 39. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 244 of 244 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Oldham County. Highest Good-day share: 2020 (91.2%, 218 of 239 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 218 | 21 | 0 | 0 | 38 | 97 |
| 2021 | 216 | 27 | 1 | 0 | 39 | 105 |
| 2022 | 221 | 22 | 2 | 0 | 41 | 112 |
| 2023 | 195 | 46 | 1 | 0 | 42 | 105 |
| 2024 | 194 | 43 | 5 | 0 | 43 | 136 |
| 2025 | 214 | 28 | 2 | 0 | 39 | 108 |
How does Oldham County compare?
How Oldham County compares
Good-day share better than typical
Oldham County 87.7%
Aiken County, South Carolina 90.6%
Typical US county 76.0%
Median AQI about typical
Oldham County 39
Aiken County, South Carolina 39
Typical US county 39
Unhealthy days / yr better than typical
Oldham County 0
Aiken County, South Carolina 0
Typical US county 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Oldham County (39), not geographic neighbors.
Aiken County, South Carolina
Median AQI 39 · 90.6% Good-day share
Albany County, New York
Median AQI 39 · 68.5% Good-day share
Anderson County, Tennessee
Median AQI 39 · 94.3% Good-day share
Bay County, Michigan
Median AQI 39 · 70.4% Good-day share
Berkeley County, West Virginia
Median AQI 39 · 83.6% Good-day share
Boyd County, Kentucky
Median AQI 39 · 80.0% Good-day share
Same primary pollutant: Ozone
Ozone led the AQI on the most monitored days here. These peers share that driver and the closest Good-day share (a second relationship type beyond median-AQI neighbors).
Chittenden County, Vermont
87.7% Good-day share · median AQI 38
El Dorado County, California
87.7% Good-day share · median AQI 40
Santa Cruz County, California
87.7% Good-day share · median AQI 35
Clay County, South Dakota
87.8% Good-day share · median AQI 34
Anne Arundel County, Maryland
87.6% Good-day share · median AQI 40
Boone County, Kentucky
87.6% Good-day share · median AQI 38
Kentucky counties on the map
Geographic containment only, other monitored counties in Kentucky, independent of AQI or pollutant match.
What Oldham 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 39 means for exposure. Health guidance
- See how Oldham County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Oldham County with its Kentucky neighbours before drawing a conclusion about the region. All of Kentucky
Based on 244 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
Keep exploring the annual AQI record
Air-quality reading list
Frequently Asked Questions
What is the air quality in Oldham County, Kentucky? ▼
Oldham County has a median Air Quality Index (AQI) of 39, rated "Good." 87.7% of monitored days (214 out of 244) had good air quality in 2025.
What is the main pollutant in Oldham County? ▼
The primary pollutant in Oldham County is Ozone (O3), which was the main AQI driver on 244 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Oldham County have? ▼
In 2025, Oldham County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 108.
Is the air quality in Oldham County getting better or worse? ▼
Air quality in Oldham County is worsening across floor-qualifying years (2020-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2020 at 91.2% (218 of 239 days). Lowest qualifying Good-day share: 2024 at 80.2% (194 of 242 days).
What does AQI 39 mean for health? ▼
Oldham County's median AQI of 39 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Oldham County compare to other counties in Kentucky? ▼
Oldham County has 87.7% good air days. Nearby counties in Kentucky: Bell (67.0% good), Boone (87.6% good), Boyd (80.0% good), Bullitt (88.4% good), Campbell (75.6% good), Carter (89.0% good).
What is the 90th percentile AQI in Oldham County? ▼
The 90th percentile AQI for Oldham County is 51, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 108 (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. Spotted a figure that looks wrong? Report a correction.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files for Oldham County, Kentucky · 2020–2025
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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.