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

Counties in Ohio by median Air Quality Index (US EPA)

Clinton County had the highest median Air Quality Index (US EPA) of 46 counties in 1991, at 61. Athens County had the lowest, at 19. The median was 36. Source: the U.S. Environmental Protection Agency.

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Highest61Clinton County
Lowest19Athens County
Median3646 counties

Map of counties, 1991

Adams County: 19 indexAllen County: 49 indexAshtabula County: 46 indexAthens County: 19 indexBelmont County: 22 indexButler County: 41 indexClark County: 50 indexClermont County: 44 indexClinton County: 61 indexColumbiana County: 28 indexCrawford County: 36 indexCuyahoga County: 51 indexFayette County: 39 indexFranklin County: 40 indexGreene County: 21 indexHamilton County: 47 indexHancock County: 29 indexJackson County: 30 indexJefferson County: 53 indexKnox County: 42 indexLake County: 33 indexLawrence County: 48 indexLicking County: 54 indexLogan County: 58 indexLorain County: 34 indexLucas County: 32 indexMadison County: 50 indexMahoning County: 33 indexMedina County: 49 indexMontgomery County: 28 indexNoble County: 29 indexOttawa County: 21 indexPickaway County: 22 indexPortage County: 54 indexPreble County: 58 indexRichland County: 23 indexSandusky County: 28 indexScioto County: 30 indexSeneca County: 21 indexStark County: 36 indexSummit County: 36 indexTrumbull County: 26 indexUnion County: 58 indexWarren County: 58 indexWashington County: 49 indexWyandot County: 21 index
  • Under 23
  • 23 to 30
  • 30 to 36
  • 36 to 47
  • 47 to 52
  • 52 and over
  • No data
index, 1991. 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, 1991

Clinton County: 61 indexClinton County61Logan County: 58 indexLogan County58Preble County: 58 indexPreble County58Union County: 58 indexUnion County58Warren County: 58 indexWarren County58Licking County: 54 indexLicking County54Portage County: 54 indexPortage County54Jefferson County: 53 indexJefferson County53Cuyahoga County: 51 indexCuyahoga County51Clark County: 50 indexClark County50Madison County: 50 indexMadison County50Allen County: 49 indexAllen County49Medina County: 49 indexMedina County49Washington County: 49 indexWashington County49Lawrence County: 48 indexLawrence County48Hamilton County: 47 indexHamilton County47Ashtabula County: 46 indexAshtabula County46Clermont County: 44 indexClermont County44Knox County: 42 indexKnox County42Butler County: 41 indexButler County41Franklin County: 40 indexFranklin County40Fayette County: 39 indexFayette County39Crawford County: 36 indexCrawford County36Stark County: 36 indexStark County36Summit County: 36 indexSummit County36Lorain County: 34 indexLorain County34Lake County: 33 indexLake County33Mahoning County: 33 indexMahoning County33Lucas County: 32 indexLucas County32Jackson County: 30 indexJackson County30Scioto County: 30 indexScioto County30Hancock County: 29 indexHancock County29Noble County: 29 indexNoble County29Columbiana County: 28 indexColumbiana County28Montgomery County: 28 indexMontgomery County28Sandusky County: 28 indexSandusky County28Trumbull County: 26 indexTrumbull County26Richland County: 23 indexRichland County23Belmont County: 22 indexBelmont County22Pickaway County: 22 indexPickaway County22Greene County: 21 indexGreene County21Ottawa County: 21 indexOttawa County21Seneca County: 21 indexSeneca County21Wyandot County: 21 indexWyandot County21Adams County: 19 indexAdams County19Athens County: 19 indexAthens County19Clinton County: 61 indexClinton County61Logan County: 58 indexLogan County58Preble County: 58 indexPreble County58Union County: 58 indexUnion County58Warren County: 58 indexWarren County58Licking County: 54 indexLicking County54Portage County: 54 indexPortage County54Jefferson County: 53 indexJefferson County53Cuyahoga County: 51 indexCuyahoga County51Clark County: 50 indexClark County50Madison County: 50 indexMadison County50Allen County: 49 indexAllen County49Medina County: 49 indexMedina County49Washington County: 49 indexWashington County49Lawrence County: 48 indexLawrence County48Hamilton County: 47 indexHamilton County47Ashtabula County: 46 indexAshtabula County46Clermont County: 44 indexClermont County44Knox County: 42 indexKnox County42Butler County: 41 indexButler County41Franklin County: 40 indexFranklin County40Fayette County: 39 indexFayette County39Crawford County: 36 indexCrawford County36Stark County: 36 indexStark County36Summit County: 36 indexSummit County36Lorain County: 34 indexLorain County34Lake County: 33 indexLake County33Mahoning County: 33 indexMahoning County33Lucas County: 32 indexLucas County32Jackson County: 30 indexJackson County30Scioto County: 30 indexScioto County30Hancock County: 29 indexHancock County29Noble County: 29 indexNoble County29Columbiana County: 28 indexColumbiana County28Montgomery County: 28 indexMontgomery County28Sandusky County: 28 indexSandusky County28Trumbull County: 26 indexTrumbull County26Richland County: 23 indexRichland County23Belmont County: 22 indexBelmont County22Pickaway County: 22 indexPickaway County22Greene County: 21 indexGreene County21Ottawa County: 21 indexOttawa County21Seneca County: 21 indexSeneca County21Wyandot County: 21 indexWyandot County21Adams County: 19 indexAdams County19Athens County: 19 indexAthens County19
index. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Retrieved 2026-10-12.

Full ranking

RankCounties1991
index		Change on 1990
1Clinton County61+17
2Logan County58+15
2Preble County58+24
2Union County58+14
2Warren County58+11
6Licking County54n/a
6Portage County54+10
8Jefferson County53+5
9Cuyahoga County510
10Clark County50+6
10Madison County50n/a
12Allen County49+8
12Medina County49+8
12Washington County49+7
15Lawrence County48+13
16Hamilton County470
17Ashtabula County46+7
18Clermont County44-2
19Knox County42+2
20Butler County41+3
21Franklin County40+5
22Fayette County390
23Crawford County36-2
23Stark County36+4
23Summit County36+1
26Lorain County34-1
27Lake County33+2
27Mahoning County33+1
29Lucas County32-1
30Jackson County30n/a
30Scioto County30+1
32Hancock County29n/a
32Noble County29+4
34Columbiana County280
34Montgomery County28+1
34Sandusky County28+4
37Trumbull County26+3
38Richland County23+3
39Belmont County22-1
39Pickaway County22+3
41Greene County21+6
41Ottawa County21-1
41Seneca County21n/a
41Wyandot County210
45Adams County190
45Athens County19n/a

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. 12 counties with data in other periods have no value for 1991 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 Ohio by median Air Quality Index (US EPA), 1991) [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 Ohio by median Air Quality Index (US EPA), 1991. 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/ohio-counties?period=1991. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: median daily AQI. Counties in Ohio by median Air Quality Index (US EPA), 1991. 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/ohio-counties?period=1991.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: median daily AQI, Counties in Ohio by median Air Quality Index (US EPA), 1991 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/median-air-quality-index/ohio-counties?period=1991 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_ohio_by_1991,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: median daily AQI: Counties in Ohio by median Air Quality Index (US EPA), 1991}},
  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/ohio-counties?period=1991. 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 Ohio by median Air Quality Index (US EPA), 1991
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/ohio-counties?period=1991
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/median-air-quality-index/ohio-counties?period=1991.
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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Rank Counties in Ohio by median Air Quality Index (US EPA) using official data, and cite the source.
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Questions

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

Clinton County, with 61 in 1991, according to the U.S. Environmental Protection Agency.

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

Athens County, with 19 in 1991.

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. 12 counties have no value for 1991 and are not ranked.

Median Air Quality Index (US EPA): other rankings

Counties in Ohio: more rankings