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

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

Hamilton County had the highest median Air Quality Index (US EPA) of 49 counties in 1999, at 71. Wyandot County had the lowest, at 19. The median was 47. Source: the U.S. Environmental Protection Agency.

Keep it in a collection in your library.
Highest71Hamilton County
Lowest19Wyandot County
Median4749 counties

Map of counties, 1999

Allen County: 45 indexAshtabula County: 46 indexAthens County: 56 indexBelmont County: 22 indexButler County: 67 indexClark County: 50 indexClermont County: 64 indexClinton County: 64 indexColumbiana County: 34 indexCrawford County: 39 indexCuyahoga County: 70 indexDelaware County: 47 indexErie County: 26 indexFayette County: 45 indexFranklin County: 69 indexGeauga County: 44 indexGreene County: 47 indexHamilton County: 71 indexHancock County: 19 indexJefferson County: 62 indexKnox County: 47 indexLake County: 45 indexLawrence County: 58 indexLicking County: 49 indexLogan County: 33 indexLorain County: 44 indexLucas County: 56 indexMadison County: 51 indexMahoning County: 64 indexMedina County: 44 indexMiami County: 47 indexMonroe County: 22 indexMontgomery County: 65 indexNoble County: 40 indexOttawa County: 19 indexPortage County: 58 indexPreble County: 54 indexRichland County: 19 indexSandusky County: 27 indexScioto County: 29 indexSeneca County: 22 indexStark County: 49 indexSummit County: 66 indexTrumbull County: 63 indexUnion County: 46 indexWarren County: 54 indexWashington County: 45 indexWood County: 44 indexWyandot County: 19 index
  • Under 27
  • 27 to 44
  • 44 to 47
  • 47 to 54
  • 54 to 64
  • 64 and over
  • No data
index, 1999. 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, 1999

Hamilton County: 71 indexHamilton County71Cuyahoga County: 70 indexCuyahoga County70Franklin County: 69 indexFranklin County69Butler County: 67 indexButler County67Summit County: 66 indexSummit County66Montgomery County: 65 indexMontgomery County65Clermont County: 64 indexClermont County64Clinton County: 64 indexClinton County64Mahoning County: 64 indexMahoning County64Trumbull County: 63 indexTrumbull County63Jefferson County: 62 indexJefferson County62Lawrence County: 58 indexLawrence County58Portage County: 58 indexPortage County58Athens County: 56 indexAthens County56Lucas County: 56 indexLucas County56Preble County: 54 indexPreble County54Warren County: 54 indexWarren County54Madison County: 51 indexMadison County51Clark County: 50 indexClark County50Licking County: 49 indexLicking County49Stark County: 49 indexStark County49Delaware County: 47 indexDelaware County47Greene County: 47 indexGreene County47Knox County: 47 indexKnox County47Miami County: 47 indexMiami County47Ashtabula County: 46 indexAshtabula County46Union County: 46 indexUnion County46Allen County: 45 indexAllen County45Fayette County: 45 indexFayette County45Lake County: 45 indexLake County45Washington County: 45 indexWashington County45Geauga County: 44 indexGeauga County44Lorain County: 44 indexLorain County44Medina County: 44 indexMedina County44Wood County: 44 indexWood County44Noble County: 40 indexNoble County40Crawford County: 39 indexCrawford County39Columbiana County: 34 indexColumbiana County34Logan County: 33 indexLogan County33Scioto County: 29 indexScioto County29Sandusky County: 27 indexSandusky County27Erie County: 26 indexErie County26Belmont County: 22 indexBelmont County22Monroe County: 22 indexMonroe County22Seneca County: 22 indexSeneca County22Hancock County: 19 indexHancock County19Ottawa County: 19 indexOttawa County19Richland County: 19 indexRichland County19Wyandot County: 19 indexWyandot County19Hamilton County: 71 indexHamilton County71Cuyahoga County: 70 indexCuyahoga County70Franklin County: 69 indexFranklin County69Butler County: 67 indexButler County67Summit County: 66 indexSummit County66Montgomery County: 65 indexMontgomery County65Clermont County: 64 indexClermont County64Clinton County: 64 indexClinton County64Mahoning County: 64 indexMahoning County64Trumbull County: 63 indexTrumbull County63Jefferson County: 62 indexJefferson County62Lawrence County: 58 indexLawrence County58Portage County: 58 indexPortage County58Athens County: 56 indexAthens County56Lucas County: 56 indexLucas County56Preble County: 54 indexPreble County54Warren County: 54 indexWarren County54Madison County: 51 indexMadison County51Clark County: 50 indexClark County50Licking County: 49 indexLicking County49Stark County: 49 indexStark County49Delaware County: 47 indexDelaware County47Greene County: 47 indexGreene County47Knox County: 47 indexKnox County47Miami County: 47 indexMiami County47Ashtabula County: 46 indexAshtabula County46Union County: 46 indexUnion County46Allen County: 45 indexAllen County45Fayette County: 45 indexFayette County45Lake County: 45 indexLake County45Washington County: 45 indexWashington County45Geauga County: 44 indexGeauga County44Lorain County: 44 indexLorain County44Medina County: 44 indexMedina County44Wood County: 44 indexWood County44Noble County: 40 indexNoble County40Crawford County: 39 indexCrawford County39Columbiana County: 34 indexColumbiana County34Logan County: 33 indexLogan County33Scioto County: 29 indexScioto County29Sandusky County: 27 indexSandusky County27Erie County: 26 indexErie County26Belmont County: 22 indexBelmont County22Monroe County: 22 indexMonroe County22Seneca County: 22 indexSeneca County22Hancock County: 19 indexHancock County19Ottawa County: 19 indexOttawa County19Richland County: 19 indexRichland County19Wyandot County: 19 indexWyandot County19
index. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Retrieved 2026-10-12.

Full ranking

RankCounties1999
index		Change on 1998
1Hamilton County71+21
2Cuyahoga County70+23
3Franklin County69+34
4Butler County67+25
5Summit County66+36
6Montgomery County65+33
7Clermont County64+10
7Clinton County640
7Mahoning County64+22
10Trumbull County63+16
11Jefferson County62+41
12Lawrence County58+12
12Portage County58+11
14Athens County56+44
14Lucas County56+22
16Preble County54+7
16Warren County540
18Madison County51-10
19Clark County50-8
20Licking County49-5
20Stark County49+16
22Delaware County47-7
22Greene County47-2
22Knox County470
22Miami County47-2
26Ashtabula County46+2
26Union County46-2
28Allen County45-4
28Fayette County45+4
28Lake County45+13
28Washington County45+1
32Geauga County44-1
32Lorain County44+11
32Medina County44-5
32Wood County44-4
36Noble County400
37Crawford County390
38Columbiana County34+7
39Logan County33-13
40Scioto County29+9
41Sandusky County27-7
42Erie County26-5
43Belmont County22+3
43Monroe County22+5
43Seneca County220
46Hancock County19-10
46Ottawa County19-2
46Richland County19-1
46Wyandot County19-2

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. 9 counties with data in other periods have no value for 1999 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), 1999) [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), 1999. 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=1999. 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), 1999. 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=1999.

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), 1999 [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=1999 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_ohio_by_1999,
  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), 1999}},
  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=1999. 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), 1999
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=1999
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/median-air-quality-index/ohio-counties?period=1999.
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)?

Hamilton County, with 71 in 1999, according to the U.S. Environmental Protection Agency.

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

Wyandot County, with 19 in 1999.

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 1999 and are not ranked.

Median Air Quality Index (US EPA): other rankings

Counties in Ohio: more rankings