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

Counties in Ohio by median Air Quality Index (US EPA), 2001

Cuyahoga County had the highest median Air Quality Index (US EPA) of 45 counties in 2001, at 72. Seneca County had the lowest, at 18. The median was 47. Source: the U.S. Environmental Protection Agency.

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Highest72Cuyahoga County
Lowest18Seneca County
Median4745 counties

Map of counties, 2001

Allen County: 43 indexAshtabula County: 45 indexAthens County: 54 indexBelmont County: 21 indexButler County: 66 indexClark County: 54 indexClermont County: 47 indexClinton County: 49 indexColumbiana County: 26 indexCrawford County: 38 indexCuyahoga County: 72 indexDelaware County: 48 indexFayette County: 38 indexFranklin County: 66 indexGeauga County: 48 indexGreene County: 46 indexHamilton County: 68 indexHancock County: 23 indexJefferson County: 66 indexKnox County: 48 indexLake County: 41 indexLawrence County: 60 indexLicking County: 45 indexLorain County: 44 indexLucas County: 63 indexMadison County: 48 indexMahoning County: 62 indexMedina County: 45 indexMiami County: 48 indexMonroe County: 24 indexMontgomery County: 65 indexNoble County: 42 indexOttawa County: 24 indexPortage County: 52 indexPreble County: 49 indexSandusky County: 21 indexScioto County: 44 indexSeneca County: 18 indexStark County: 47 indexSummit County: 64 indexTrumbull County: 61 indexWarren County: 45 indexWashington County: 44 indexWood County: 44 indexWyandot County: 20 index
  • Under 30
  • 30 to 44
  • 44 to 47
  • 47 to 49
  • 49 to 63
  • 63 and over
  • No data
index, 2001. 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, 2001

Cuyahoga County: 72 indexCuyahoga County72Hamilton County: 68 indexHamilton County68Butler County: 66 indexButler County66Franklin County: 66 indexFranklin County66Jefferson County: 66 indexJefferson County66Montgomery County: 65 indexMontgomery County65Summit County: 64 indexSummit County64Lucas County: 63 indexLucas County63Mahoning County: 62 indexMahoning County62Trumbull County: 61 indexTrumbull County61Lawrence County: 60 indexLawrence County60Athens County: 54 indexAthens County54Clark County: 54 indexClark County54Portage County: 52 indexPortage County52Clinton County: 49 indexClinton County49Preble County: 49 indexPreble County49Delaware County: 48 indexDelaware County48Geauga County: 48 indexGeauga County48Knox County: 48 indexKnox County48Madison County: 48 indexMadison County48Miami County: 48 indexMiami County48Clermont County: 47 indexClermont County47Stark County: 47 indexStark County47Greene County: 46 indexGreene County46Ashtabula County: 45 indexAshtabula County45Licking County: 45 indexLicking County45Medina County: 45 indexMedina County45Warren County: 45 indexWarren County45Lorain County: 44 indexLorain County44Scioto County: 44 indexScioto County44Washington County: 44 indexWashington County44Wood County: 44 indexWood County44Allen County: 43 indexAllen County43Noble County: 42 indexNoble County42Lake County: 41 indexLake County41Crawford County: 38 indexCrawford County38Fayette County: 38 indexFayette County38Columbiana County: 26 indexColumbiana County26Monroe County: 24 indexMonroe County24Ottawa County: 24 indexOttawa County24Hancock County: 23 indexHancock County23Belmont County: 21 indexBelmont County21Sandusky County: 21 indexSandusky County21Wyandot County: 20 indexWyandot County20Seneca County: 18 indexSeneca County18Cuyahoga County: 72 indexCuyahoga County72Hamilton County: 68 indexHamilton County68Butler County: 66 indexButler County66Franklin County: 66 indexFranklin County66Jefferson County: 66 indexJefferson County66Montgomery County: 65 indexMontgomery County65Summit County: 64 indexSummit County64Lucas County: 63 indexLucas County63Mahoning County: 62 indexMahoning County62Trumbull County: 61 indexTrumbull County61Lawrence County: 60 indexLawrence County60Athens County: 54 indexAthens County54Clark County: 54 indexClark County54Portage County: 52 indexPortage County52Clinton County: 49 indexClinton County49Preble County: 49 indexPreble County49Delaware County: 48 indexDelaware County48Geauga County: 48 indexGeauga County48Knox County: 48 indexKnox County48Madison County: 48 indexMadison County48Miami County: 48 indexMiami County48Clermont County: 47 indexClermont County47Stark County: 47 indexStark County47Greene County: 46 indexGreene County46Ashtabula County: 45 indexAshtabula County45Licking County: 45 indexLicking County45Medina County: 45 indexMedina County45Warren County: 45 indexWarren County45Lorain County: 44 indexLorain County44Scioto County: 44 indexScioto County44Washington County: 44 indexWashington County44Wood County: 44 indexWood County44Allen County: 43 indexAllen County43Noble County: 42 indexNoble County42Lake County: 41 indexLake County41Crawford County: 38 indexCrawford County38Fayette County: 38 indexFayette County38Columbiana County: 26 indexColumbiana County26Monroe County: 24 indexMonroe County24Ottawa County: 24 indexOttawa County24Hancock County: 23 indexHancock County23Belmont County: 21 indexBelmont County21Sandusky County: 21 indexSandusky County21Wyandot County: 20 indexWyandot County20Seneca County: 18 indexSeneca County18
index. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Retrieved 2026-10-12.

Full ranking

RankCounties2001
index		Change on 2000
1Cuyahoga County72+1
2Hamilton County680
3Butler County66+2
3Franklin County660
3Jefferson County66+3
6Montgomery County65-1
7Summit County640
8Lucas County63+6
9Mahoning County62+1
10Trumbull County61+1
11Lawrence County60+2
12Athens County540
12Clark County54+3
14Portage County52-1
15Clinton County49-1
15Preble County490
17Delaware County48+3
17Geauga County48+3
17Knox County48+3
17Madison County480
17Miami County48+2
22Clermont County47-1
22Stark County47+2
24Greene County46+3
25Ashtabula County45+1
25Licking County450
25Medina County45+2
25Warren County450
29Lorain County44+5
29Scioto County44+23
29Washington County44+2
29Wood County44+3
33Allen County43+1
34Noble County42+2
35Lake County41+1
36Crawford County38+2
36Fayette County38-1
38Columbiana County26-5
39Monroe County24+3
39Ottawa County24+2
41Hancock County23-2
42Belmont County21-3
42Sandusky County21-1
44Wyandot County20+1
45Seneca County180

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. 13 counties with data in other periods have no value for 2001 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), 2001) [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), 2001. 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. 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), 2001. 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.

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), 2001 [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 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_ohio_by_2001,
  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), 2001}},
  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. 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), 2001
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
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/median-air-quality-index/ohio-counties.
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)?

Cuyahoga County, with 72 in 2001, according to the U.S. Environmental Protection Agency.

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

Seneca County, with 18 in 2001.

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. 13 counties have no value for 2001 and are not ranked.

Median Air Quality Index (US EPA): other rankings

Counties in Ohio: more rankings