Kentucky · County air quality · 2025
Jefferson County, Kentucky
Median AQI 49 (Good). 51.5% of monitored days rated Good, direct from EPA Air Quality System stations.
- 49
- Median AQI
- 51.5%
- Good-air days
- 1
- Unhealthy days
- 7%
- Cleaner than US counties
Jefferson County's 2025 annual median AQI is 49 (Good), with 51.5% Good days
According to the U.S. EPA Air Quality System, Jefferson County, Kentucky posted a 2025 median AQI of 49 (Good) across 365 monitored days, with 51.5% rated Good and 1 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Jefferson County's 51.5% Good-day share places it cleaner than 7% of US counties in 2025.
- Closest median-AQI peer
- Adams County (55.1% Good, median AQI 49) is the closest nationwide median-AQI peer to Jefferson County.
- 2020–2025 trend
- Jefferson County's floor-qualifying Good-day share is improving from 2020 to 2025 (41.3% → 51.5%).
- Median AQI
- Median AQI: 49
According to the 2025 EPA AQS county release on PlainAirData, Jefferson County, Kentucky ranks #866 of 951 by median AQI (49) and #882 by good-day share (51.5%). Ponce County, Puerto Rico is #1 of 951 by median AQI (3, 91.4% Good days) at good-day-share #159 ≠ largest of 7 at 100.0% Good days #1 by good-day share (100.0%, median AQI 9) at median-AQI #7.
Data updated August 2026
- Good · 188 d · 51.5%
- Moderate · 167 d · 45.8%
- USG · 9 d · 2.5%
- Unhealthy · 1 d · 0.3%
How did Jefferson County's air break down in 2025?
Across 365 monitored days, 188 fell in the Good band (AQI 0–50) and 1 reached Unhealthy or worse. The worst single day peaked at AQI 153 (Unhealthy).
EPA AQS →Share of monitored days at AQI 0-50 (Good band).
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
Where Jefferson County sits nationally
COUNT-derived placement among 951 US counties with at least 100 monitored days in 2025. Jefferson County's Good-day share is 51.5% - cleaner than 7% of that comparison set.
Jefferson County Good-day share vs. every US county
Share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release
51.5% 7th percentile higher than 7% of 951 US counties
Each bar is a band; taller bars hold more US counties. 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
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Jefferson County.
- PM2.5 · 213 days · 58.4%
- Ozone · 147 days · 40.3%
- NO₂ · 5 days · 1.4%
2024 daily-monitor rhythm in Jefferson County
Month-by-month median AQI from EPA day-level county monitors (366 reported days in 2024). Jul posted the highest typical readings (median AQI 59, peak 108); Dec was cleanest at median 40. Summer months (Jun–Aug) averaged median AQI 56 vs 45 in Dec–Feb. 1 day crossed Unhealthy (AQI >150) at least once that year.
Five-year seasonal record
EPA day-level county files · 2020–20241,827 daily readings show a recurring local pattern: Jun has the highest matched-month median AQI (64), while Mar is lowest (50). Each cell is that month’s median daily AQI, not a current-air forecast.
Lower AQI is better. The colors summarize EPA AQI bands; gaps mean the county had no day-level record for that month.
Health Impact Assessment
Jefferson County's air quality is rated Moderate based on 51.5% good air days. There were 1 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 9 days reached "Unhealthy for Sensitive Groups" (AQI 101-150) and peak AQI reached 153. Sensitive groups should monitor real-time conditions at AirNow.gov.
The dominant pollutant is PM2.5, driving AQI on 213 of 365 monitored days.
5-Year Air Quality Trend
Air quality is improving in Jefferson County. Highest Good-day share: 2025 (51.5%, 188 of 365 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 151 | 208 | 7 | 0 | 52 | 115 |
| 2021 | 138 | 221 | 6 | 0 | 54 | 126 |
| 2022 | 147 | 211 | 7 | 0 | 53 | 136 |
| 2023 | 123 | 226 | 15 | 1 | 55 | 171 |
| 2024 | 186 | 168 | 11 | 1 | 50 | 156 |
| 2025 | 188 | 167 | 9 | 1 | 49 | 153 |
How does Jefferson County compare?
How Jefferson County compares
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 Jefferson County, Kentucky · 2020–2025
Download this county's annual AQI row as CSV , with the same EPA fields and denominator shown on this page.
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.