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 49 counties in 1998, at 64. Athens County had the lowest, at 12. The median was 42. Source: the U.S. Environmental Protection Agency.

Keep it in a collection in your library.
Highest64Clinton County
Lowest12Athens County
Median4249 counties

Map of counties, 1998

Allen County: 49 indexAshtabula County: 44 indexAthens County: 12 indexBelmont County: 19 indexButler County: 42 indexClark County: 58 indexClermont County: 54 indexClinton County: 64 indexColumbiana County: 27 indexCrawford County: 39 indexCuyahoga County: 47 indexDelaware County: 54 indexErie County: 31 indexFayette County: 41 indexFranklin County: 35 indexGeauga County: 45 indexGreene County: 49 indexHamilton County: 50 indexHancock County: 29 indexJefferson County: 21 indexKnox County: 47 indexLake County: 32 indexLawrence County: 46 indexLicking County: 54 indexLogan County: 46 indexLorain County: 33 indexLucas County: 34 indexMadison County: 61 indexMahoning County: 42 indexMedina County: 49 indexMiami County: 49 indexMonroe County: 17 indexMontgomery County: 32 indexNoble County: 40 indexOttawa County: 21 indexPortage County: 47 indexPreble County: 47 indexRichland County: 20 indexSandusky County: 34 indexScioto County: 20 indexSeneca County: 22 indexStark County: 33 indexSummit County: 30 indexTrumbull County: 47 indexUnion County: 48 indexWarren County: 54 indexWashington County: 44 indexWood County: 48 indexWyandot County: 21 index
  • Under 22
  • 22 to 33
  • 33 to 42
  • 42 to 47
  • 47 to 49
  • 49 and over
  • No data
index, 1998. 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, 1998

Clinton County: 64 indexClinton County64Madison County: 61 indexMadison County61Clark County: 58 indexClark County58Clermont County: 54 indexClermont County54Delaware County: 54 indexDelaware County54Licking County: 54 indexLicking County54Warren County: 54 indexWarren County54Hamilton County: 50 indexHamilton County50Allen County: 49 indexAllen County49Greene County: 49 indexGreene County49Medina County: 49 indexMedina County49Miami County: 49 indexMiami County49Union County: 48 indexUnion County48Wood County: 48 indexWood County48Cuyahoga County: 47 indexCuyahoga County47Knox County: 47 indexKnox County47Portage County: 47 indexPortage County47Preble County: 47 indexPreble County47Trumbull County: 47 indexTrumbull County47Lawrence County: 46 indexLawrence County46Logan County: 46 indexLogan County46Geauga County: 45 indexGeauga County45Ashtabula County: 44 indexAshtabula County44Washington County: 44 indexWashington County44Butler County: 42 indexButler County42Mahoning County: 42 indexMahoning County42Fayette County: 41 indexFayette County41Noble County: 40 indexNoble County40Crawford County: 39 indexCrawford County39Franklin County: 35 indexFranklin County35Lucas County: 34 indexLucas County34Sandusky County: 34 indexSandusky County34Lorain County: 33 indexLorain County33Stark County: 33 indexStark County33Lake County: 32 indexLake County32Montgomery County: 32 indexMontgomery County32Erie County: 31 indexErie County31Summit County: 30 indexSummit County30Hancock County: 29 indexHancock County29Columbiana County: 27 indexColumbiana County27Seneca County: 22 indexSeneca County22Jefferson County: 21 indexJefferson County21Ottawa County: 21 indexOttawa County21Wyandot County: 21 indexWyandot County21Richland County: 20 indexRichland County20Scioto County: 20 indexScioto County20Belmont County: 19 indexBelmont County19Monroe County: 17 indexMonroe County17Athens County: 12 indexAthens County12Clinton County: 64 indexClinton County64Madison County: 61 indexMadison County61Clark County: 58 indexClark County58Clermont County: 54 indexClermont County54Delaware County: 54 indexDelaware County54Licking County: 54 indexLicking County54Warren County: 54 indexWarren County54Hamilton County: 50 indexHamilton County50Allen County: 49 indexAllen County49Greene County: 49 indexGreene County49Medina County: 49 indexMedina County49Miami County: 49 indexMiami County49Union County: 48 indexUnion County48Wood County: 48 indexWood County48Cuyahoga County: 47 indexCuyahoga County47Knox County: 47 indexKnox County47Portage County: 47 indexPortage County47Preble County: 47 indexPreble County47Trumbull County: 47 indexTrumbull County47Lawrence County: 46 indexLawrence County46Logan County: 46 indexLogan County46Geauga County: 45 indexGeauga County45Ashtabula County: 44 indexAshtabula County44Washington County: 44 indexWashington County44Butler County: 42 indexButler County42Mahoning County: 42 indexMahoning County42Fayette County: 41 indexFayette County41Noble County: 40 indexNoble County40Crawford County: 39 indexCrawford County39Franklin County: 35 indexFranklin County35Lucas County: 34 indexLucas County34Sandusky County: 34 indexSandusky County34Lorain County: 33 indexLorain County33Stark County: 33 indexStark County33Lake County: 32 indexLake County32Montgomery County: 32 indexMontgomery County32Erie County: 31 indexErie County31Summit County: 30 indexSummit County30Hancock County: 29 indexHancock County29Columbiana County: 27 indexColumbiana County27Seneca County: 22 indexSeneca County22Jefferson County: 21 indexJefferson County21Ottawa County: 21 indexOttawa County21Wyandot County: 21 indexWyandot County21Richland County: 20 indexRichland County20Scioto County: 20 indexScioto County20Belmont County: 19 indexBelmont County19Monroe County: 17 indexMonroe County17Athens County: 12 indexAthens County12
index. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Retrieved 2026-10-12.

Full ranking

RankCounties1998
index		Change on 1997
1Clinton County64+17
2Madison County61+15
3Clark County58+9
4Clermont County54+9
4Delaware County54+10
4Licking County54+10
4Warren County54+9
8Hamilton County50+4
9Allen County49+7
9Greene County49+4
9Medina County49+5
9Miami County49+5
13Union County48+15
13Wood County48+7
15Cuyahoga County47+1
15Knox County47+4
15Portage County47+3
15Preble County47+1
15Trumbull County47+3
20Lawrence County46+2
20Logan County46+2
22Geauga County450
23Ashtabula County44+2
23Washington County44+6
25Butler County42+3
25Mahoning County42+6
27Fayette County41+3
28Noble County40-1
29Crawford County39+4
30Franklin County35+3
31Lucas County34+4
31Sandusky County34-3
33Lorain County33+1
33Stark County33+1
35Lake County32+1
35Montgomery County32+3
37Erie County31n/a
38Summit County30+2
39Hancock County29+1
40Columbiana County270
41Seneca County22+1
42Jefferson County21-17
42Ottawa County210
42Wyandot County210
45Richland County200
45Scioto County200
47Belmont County19-4
48Monroe County17-4
49Athens County12-6

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. 9 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: 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), 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: median daily AQI, Counties in Ohio by median 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/median-air-quality-index/ohio-counties?period=1998. 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), 1998. 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=1998.

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), 1998 [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=1998 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_ohio_by_1998,
  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), 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/median-air-quality-index/ohio-counties?period=1998. 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), 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/median-air-quality-index/ohio-counties?period=1998
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/median-air-quality-index/ohio-counties?period=1998.
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)?

Clinton County, with 64 in 1998, according to the U.S. Environmental Protection Agency.

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

Athens County, with 12 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: median daily AQI. Retrieved 2026-10-12. 9 counties have no value for 1998 and are not ranked.

Median Air Quality Index (US EPA): other rankings

Counties in Ohio: more rankings