Counties in Kentucky by highest daily Air Quality Index (US EPA)

Jefferson County had the highest highest daily Air Quality Index (US EPA) of 37 counties in 1998, at 218. Floyd County had the lowest, at 36. The median was 192. Source: the U.S. Environmental Protection Agency.

Highest218Jefferson County

Lowest36Floyd County

Median19237 counties

Map of counties, 1998

Under 130
130 to 180
180 to 190
190 to 200
200 and over
No data

index, 1998. Hatched areas have no value for this period. Source: EPA, EPA AirData annual AQI by county: highest daily AQI. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 1998

index. Source: EPA, EPA AirData annual AQI by county: highest daily AQI. Retrieved 2026-10-12.

Full ranking

Rank	Counties	1998 index	Change on 1997
1	Jefferson County	218	+18
2	Greenup County	214	+50
3	Washington County	208	+34
4	Oldham County	207	+3
5	Fayette County	206	+32
5	Livingston County	206	+14
7	Daviess County	204	+22
7	Hancock County	204	+30
9	Kenton County	203	+29
10	Simpson County	201	-5
11	Carter County	197	n/a
11	Scott County	197	+82
13	Boone County	195	+45
13	Campbell County	195	+3
13	Christian County	195	+45
13	Edmonson County	195	+13
13	McLean County	195	+34
18	Boyd County	192	-15
18	Bullitt County	192	-14
18	Jessamine County	192	+13
18	Lawrence County	192	+84
18	Trigg County	192	+26
23	Morgan County	190	+50
24	Graves County	187	+31
25	McCracken County	182	-3
26	Henderson County	177	+11
27	Bell County	174	+52
28	Pike County	172	+75
28	Pulaski County	172	+32
30	Hardin County	164	+52
31	Perry County	133	+53
32	Marshall County	65	0
33	Madison County	55	+5
34	Harlan County	48	-4
35	Whitley County	43	-9
36	Warren County	42	-6
37	Floyd County	36	-16

Other periods

About this ranking

Highest daily Air Quality Index (AQI) value recorded in a US county during the year, from the EPA AirData annual summaries. Values above 500 are beyond the AQI scale and are published as EPA computes them.

A single day decides the value, so one wildfire or dust event can set it. Dust from the dry Owens Lake bed puts Inyo and Mono counties in California in the thousands. 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. 18 counties with data in other periods have no value for 1998 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: highest 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: highest daily AQI (Counties in Kentucky by highest daily Air Quality Index (US EPA), 1998) [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: highest daily AQI, Counties in Kentucky by highest daily Air Quality Index (US EPA), 1998. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/highest-daily-air-quality-index/kentucky-counties?period=1998. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: highest daily AQI. Counties in Kentucky by highest daily Air Quality Index (US EPA), 1998. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/highest-daily-air-quality-index/kentucky-counties?period=1998.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: highest daily AQI, Counties in Kentucky by highest daily Air Quality Index (US EPA), 1998 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/highest-daily-air-quality-index/kentucky-counties?period=1998 (Accessed: 12 October 2026).

BibTeX

@misc{environmental_counties_in_kentucky_by_1998,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: highest daily AQI: Counties in Kentucky by highest daily Air Quality Index (US EPA), 1998}},
  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/highest-daily-air-quality-index/kentucky-counties?period=1998. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: highest 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: highest daily AQI: Counties in Kentucky by highest daily Air Quality Index (US EPA), 1998
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/highest-daily-air-quality-index/kentucky-counties?period=1998
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/highest-daily-air-quality-index/kentucky-counties?period=1998.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: highest 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 highest daily Air Quality Index (US EPA)?

Jefferson County, with 218 in 1998, according to the U.S. Environmental Protection Agency.

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

Floyd County, with 36 in 1998.

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: highest daily AQI. Retrieved 2026-10-12. 18 counties have no value for 1998 and are not ranked.