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

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

Clark County had the highest median Air Quality Index (US EPA) of 48 counties in 1997, at 49. Athens County had the lowest, at 18. The median was 39. Source: the U.S. Environmental Protection Agency.

Keep it in a collection in your library.
Highest49Clark County
Lowest18Athens County
Median3948 counties

Map of counties, 1997

Allen County: 42 indexAshtabula County: 42 indexAthens County: 18 indexBelmont County: 23 indexButler County: 39 indexClark County: 49 indexClermont County: 45 indexClinton County: 47 indexColumbiana County: 27 indexCrawford County: 35 indexCuyahoga County: 46 indexDelaware County: 44 indexFayette County: 38 indexFranklin County: 32 indexGeauga County: 45 indexGreene County: 45 indexHamilton County: 46 indexHancock County: 28 indexJefferson County: 38 indexKnox County: 43 indexLake County: 31 indexLawrence County: 44 indexLicking County: 44 indexLogan County: 44 indexLorain County: 32 indexLucas County: 30 indexMadison County: 46 indexMahoning County: 36 indexMedina County: 44 indexMiami County: 44 indexMonroe County: 21 indexMontgomery County: 29 indexNoble County: 41 indexOttawa County: 21 indexPortage County: 44 indexPreble County: 46 indexRichland County: 20 indexSandusky County: 37 indexScioto County: 20 indexSeneca County: 21 indexStark County: 32 indexSummit County: 28 indexTrumbull County: 44 indexUnion County: 33 indexWarren County: 45 indexWashington County: 38 indexWood County: 41 indexWyandot County: 21 index
  • Under 26
  • 26 to 32
  • 32 to 39
  • 39 to 44
  • 44 to 45
  • 45 and over
  • No data
index, 1997. 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, 1997

Clark County: 49 indexClark County49Clinton County: 47 indexClinton County47Cuyahoga County: 46 indexCuyahoga County46Hamilton County: 46 indexHamilton County46Madison County: 46 indexMadison County46Preble County: 46 indexPreble County46Clermont County: 45 indexClermont County45Geauga County: 45 indexGeauga County45Greene County: 45 indexGreene County45Warren County: 45 indexWarren County45Delaware County: 44 indexDelaware County44Lawrence County: 44 indexLawrence County44Licking County: 44 indexLicking County44Logan County: 44 indexLogan County44Medina County: 44 indexMedina County44Miami County: 44 indexMiami County44Portage County: 44 indexPortage County44Trumbull County: 44 indexTrumbull County44Knox County: 43 indexKnox County43Allen County: 42 indexAllen County42Ashtabula County: 42 indexAshtabula County42Noble County: 41 indexNoble County41Wood County: 41 indexWood County41Butler County: 39 indexButler County39Fayette County: 38 indexFayette County38Jefferson County: 38 indexJefferson County38Washington County: 38 indexWashington County38Sandusky County: 37 indexSandusky County37Mahoning County: 36 indexMahoning County36Crawford County: 35 indexCrawford County35Union County: 33 indexUnion County33Franklin County: 32 indexFranklin County32Lorain County: 32 indexLorain County32Stark County: 32 indexStark County32Lake County: 31 indexLake County31Lucas County: 30 indexLucas County30Montgomery County: 29 indexMontgomery County29Hancock County: 28 indexHancock County28Summit County: 28 indexSummit County28Columbiana County: 27 indexColumbiana County27Belmont County: 23 indexBelmont County23Monroe County: 21 indexMonroe County21Ottawa County: 21 indexOttawa County21Seneca County: 21 indexSeneca County21Wyandot County: 21 indexWyandot County21Richland County: 20 indexRichland County20Scioto County: 20 indexScioto County20Athens County: 18 indexAthens County18Clark County: 49 indexClark County49Clinton County: 47 indexClinton County47Cuyahoga County: 46 indexCuyahoga County46Hamilton County: 46 indexHamilton County46Madison County: 46 indexMadison County46Preble County: 46 indexPreble County46Clermont County: 45 indexClermont County45Geauga County: 45 indexGeauga County45Greene County: 45 indexGreene County45Warren County: 45 indexWarren County45Delaware County: 44 indexDelaware County44Lawrence County: 44 indexLawrence County44Licking County: 44 indexLicking County44Logan County: 44 indexLogan County44Medina County: 44 indexMedina County44Miami County: 44 indexMiami County44Portage County: 44 indexPortage County44Trumbull County: 44 indexTrumbull County44Knox County: 43 indexKnox County43Allen County: 42 indexAllen County42Ashtabula County: 42 indexAshtabula County42Noble County: 41 indexNoble County41Wood County: 41 indexWood County41Butler County: 39 indexButler County39Fayette County: 38 indexFayette County38Jefferson County: 38 indexJefferson County38Washington County: 38 indexWashington County38Sandusky County: 37 indexSandusky County37Mahoning County: 36 indexMahoning County36Crawford County: 35 indexCrawford County35Union County: 33 indexUnion County33Franklin County: 32 indexFranklin County32Lorain County: 32 indexLorain County32Stark County: 32 indexStark County32Lake County: 31 indexLake County31Lucas County: 30 indexLucas County30Montgomery County: 29 indexMontgomery County29Hancock County: 28 indexHancock County28Summit County: 28 indexSummit County28Columbiana County: 27 indexColumbiana County27Belmont County: 23 indexBelmont County23Monroe County: 21 indexMonroe County21Ottawa County: 21 indexOttawa County21Seneca County: 21 indexSeneca County21Wyandot County: 21 indexWyandot County21Richland County: 20 indexRichland County20Scioto County: 20 indexScioto County20Athens County: 18 indexAthens County18
index. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Retrieved 2026-10-12.

Full ranking

RankCounties1997
index		Change on 1996
1Clark County490
2Clinton County47-2
3Cuyahoga County46-1
3Hamilton County46-1
3Madison County46-4
3Preble County46+1
7Clermont County45-2
7Geauga County45n/a
7Greene County45+26
7Warren County45-1
11Delaware County44n/a
11Lawrence County44+2
11Licking County44-4
11Logan County440
11Medina County440
11Miami County44-3
11Portage County44-1
11Trumbull County440
19Knox County43-2
20Allen County42-3
20Ashtabula County42+2
22Noble County41+13
22Wood County41n/a
24Butler County390
25Fayette County38-6
25Jefferson County38-2
25Washington County38-4
28Sandusky County37+1
29Mahoning County36-1
30Crawford County35+13
31Union County33n/a
32Franklin County320
32Lorain County32-4
32Stark County32-1
35Lake County31-1
36Lucas County30-3
37Montgomery County29-1
38Hancock County28+4
38Summit County28-4
40Columbiana County27-5
41Belmont County23-1
42Monroe County21-4
42Ottawa County210
42Seneca County21+2
42Wyandot County210
46Richland County200
46Scioto County20-2
48Athens County18+2

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. 10 counties with data in other periods have no value for 1997 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), 1997) [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), 1997. 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=1997. 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), 1997. 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=1997.

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), 1997 [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=1997 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_ohio_by_1997,
  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), 1997}},
  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=1997. 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), 1997
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=1997
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/median-air-quality-index/ohio-counties?period=1997.
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)?

Clark County, with 49 in 1997, according to the U.S. Environmental Protection Agency.

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

Athens County, with 18 in 1997.

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. 10 counties have no value for 1997 and are not ranked.

Median Air Quality Index (US EPA): other rankings

Counties in Ohio: more rankings