Data / Rankings / Median Air Quality Index (US EPA) / Counties in Kentucky

Counties in Kentucky by median Air Quality Index (US EPA), 2004

Jefferson County had the highest median Air Quality Index (US EPA) of 36 counties in 2004, at 61. Marshall County had the lowest, at 17. The median was 42. Source: the U.S. Environmental Protection Agency.

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Highest61Jefferson County
Lowest17Marshall County
Median4236 counties

Map of counties, 2004

Bell County: 44 indexBoone County: 40 indexBoyd County: 43 indexBullitt County: 41 indexCampbell County: 43 indexCarter County: 43 indexChristian County: 50 indexDaviess County: 40 indexEdmonson County: 44 indexFayette County: 41 indexFranklin County: 55 indexGraves County: 39 indexGreenup County: 42 indexHancock County: 42 indexHardin County: 46 indexHarlan County: 19 indexHenderson County: 41 indexJefferson County: 61 indexJessamine County: 40 indexKenton County: 48 indexLaurel County: 58 indexLivingston County: 44 indexMcCracken County: 42 indexMcLean County: 44 indexMadison County: 56 indexMarshall County: 17 indexMorgan County: 38 indexOldham County: 44 indexPerry County: 44 indexPike County: 38 indexPulaski County: 41 indexScott County: 33 indexSimpson County: 42 indexTrigg County: 42 indexWarren County: 44 indexWashington County: 37 index
  • Under 39
  • 39 to 41
  • 41 to 42
  • 42 to 44
  • 44 to 46
  • 46 and over
  • No data
index, 2004. Hatched areas have no value for this period. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2004

Jefferson County: 61 indexJefferson County61Laurel County: 58 indexLaurel County58Madison County: 56 indexMadison County56Franklin County: 55 indexFranklin County55Christian County: 50 indexChristian County50Kenton County: 48 indexKenton County48Hardin County: 46 indexHardin County46Bell County: 44 indexBell County44Edmonson County: 44 indexEdmonson County44Livingston County: 44 indexLivingston County44McLean County: 44 indexMcLean County44Oldham County: 44 indexOldham County44Perry County: 44 indexPerry County44Warren County: 44 indexWarren County44Boyd County: 43 indexBoyd County43Campbell County: 43 indexCampbell County43Carter County: 43 indexCarter County43Greenup County: 42 indexGreenup County42Hancock County: 42 indexHancock County42McCracken County: 42 indexMcCracken County42Simpson County: 42 indexSimpson County42Trigg County: 42 indexTrigg County42Bullitt County: 41 indexBullitt County41Fayette County: 41 indexFayette County41Henderson County: 41 indexHenderson County41Pulaski County: 41 indexPulaski County41Boone County: 40 indexBoone County40Daviess County: 40 indexDaviess County40Jessamine County: 40 indexJessamine County40Graves County: 39 indexGraves County39Morgan County: 38 indexMorgan County38Pike County: 38 indexPike County38Washington County: 37 indexWashington County37Scott County: 33 indexScott County33Harlan County: 19 indexHarlan County19Marshall County: 17 indexMarshall County17Jefferson County: 61 indexJefferson County61Laurel County: 58 indexLaurel County58Madison County: 56 indexMadison County56Franklin County: 55 indexFranklin County55Christian County: 50 indexChristian County50Kenton County: 48 indexKenton County48Hardin County: 46 indexHardin County46Bell County: 44 indexBell County44Edmonson County: 44 indexEdmonson County44Livingston County: 44 indexLivingston County44McLean County: 44 indexMcLean County44Oldham County: 44 indexOldham County44Perry County: 44 indexPerry County44Warren County: 44 indexWarren County44Boyd County: 43 indexBoyd County43Campbell County: 43 indexCampbell County43Carter County: 43 indexCarter County43Greenup County: 42 indexGreenup County42Hancock County: 42 indexHancock County42McCracken County: 42 indexMcCracken County42Simpson County: 42 indexSimpson County42Trigg County: 42 indexTrigg County42Bullitt County: 41 indexBullitt County41Fayette County: 41 indexFayette County41Henderson County: 41 indexHenderson County41Pulaski County: 41 indexPulaski County41Boone County: 40 indexBoone County40Daviess County: 40 indexDaviess County40Jessamine County: 40 indexJessamine County40Graves County: 39 indexGraves County39Morgan County: 38 indexMorgan County38Pike County: 38 indexPike County38Washington County: 37 indexWashington County37Scott County: 33 indexScott County33Harlan County: 19 indexHarlan County19Marshall County: 17 indexMarshall County17
index. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Retrieved 2026-10-12.

Full ranking

RankCounties2004
index		Change on 2003
1Jefferson County61-2
2Laurel County58+1
3Madison County56+2
4Franklin County550
5Christian County50-4
6Kenton County48+2
7Hardin County46-3
8Bell County44-2
8Edmonson County44+1
8Livingston County44-4
8McLean County44-1
8Oldham County44+1
8Perry County440
8Warren County44-2
15Boyd County43-5
15Campbell County430
15Carter County43-4
18Greenup County42-2
18Hancock County42-4
18McCracken County42-2
18Simpson County42-2
18Trigg County42-2
23Bullitt County41+1
23Fayette County41-3
23Henderson County41-5
23Pulaski County41-1
27Boone County400
27Daviess County40+1
27Jessamine County40-3
30Graves County39-5
31Morgan County38-1
31Pike County380
33Washington County37-3
34Scott County33-4
35Harlan County19-2
36Marshall County17-1

Other periods

About this ranking

Median of the daily Air Quality Index (AQI) values of a US county over the days of the year with an AQI, from the EPA AirData annual summaries.

More on how it is measured
  • The daily county AQI is the highest AQI among the monitors and pollutants reported that day (ozone, PM2.5, PM10, carbon monoxide and nitrogen dioxide).
  • Lower is cleaner: 0 to 50 is good, 51 to 100 moderate and above 100 unhealthy for sensitive groups.

United States counties with air quality monitors only, about 1,000 of some 3,100 in recent years; a county without monitors has no value. The number of days with an AQI differs between counties because some monitors run only in the ozone season.

Every value in the ranking comes from the same publisher and the same period, so the counties are compared on one definition. 19 counties with data in other periods have no value for 2004 and are left out rather than filled from another source. Equal values share a rank.

How to cite

U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.

Citation styles

The publisher is the author. Invokely is named only as the place the figures were read, where a style asks for it.

APA 7

U.S. Environmental Protection Agency. (2026). EPA AirData annual AQI by county: median daily AQI (Counties in Kentucky by median Air Quality Index (US EPA), 2004) [Data set]. Retrieved October 12, 2026, from https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual

MLA 9

EPA AirData annual AQI by county: median daily AQI, Counties in Kentucky by median Air Quality Index (US EPA), 2004. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/median-air-quality-index/kentucky-counties. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: median daily AQI. Counties in Kentucky by median Air Quality Index (US EPA), 2004. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/median-air-quality-index/kentucky-counties.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: median daily AQI, Counties in Kentucky by median Air Quality Index (US EPA), 2004 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/median-air-quality-index/kentucky-counties (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_kentucky_by_2004,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: median daily AQI: Counties in Kentucky by median Air Quality Index (US EPA), 2004}},
  year = {2026},
  howpublished = {Data set},
  url = {https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual},
  urldate = {2026-10-12},
  note = {Accessed via Invokely, https://invokely.ai/rankings/median-air-quality-index/kentucky-counties. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download\_files.html\#Annual. Retrieved 2026-10-12.},
}
RIS
TY  - DATA
AU  - U.S. Environmental Protection Agency
TI  - EPA AirData annual AQI by county: median daily AQI: Counties in Kentucky by median Air Quality Index (US EPA), 2004
PY  - 2026
DA  - 2026/07/13
PB  - U.S. Environmental Protection Agency
DB  - Invokely
UR  - https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual
L2  - https://invokely.ai/rankings/median-air-quality-index/kentucky-counties
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/median-air-quality-index/kentucky-counties.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
ER  -
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Questions

Which county has the highest median Air Quality Index (US EPA)?

Jefferson County, with 61 in 2004, according to the U.S. Environmental Protection Agency.

Which county has the lowest median Air Quality Index (US EPA)?

Marshall County, with 17 in 2004.

Where does this ranking come from?

Every value comes from one source and one period, so the places are comparable: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: median daily AQI. Retrieved 2026-10-12. 19 counties have no value for 2004 and are not ranked.

Median Air Quality Index (US EPA): other rankings

Counties in Kentucky: more rankings