Data / Rankings / Share of days with good air quality (US EPA AQI) / Counties in Ohio

Counties in Ohio by share of days with good air quality (US EPA AQI), 2001

Hancock County had the highest share of days with good air quality (US EPA AQI) of 45 counties in 2001, at 100%. Hamilton County had the lowest, at 11.2%. The median was 57.9%. Source: EPA.

Highest100Hancock County
Lowest11.2Hamilton County
Median57.945 counties

All counties, 2001

Hancock County: 100 %Hancock County100Ottawa County: 100 %Ottawa County100Sandusky County: 100 %Sandusky County100Belmont County: 98.3 %Belmont County98.3Seneca County: 97.7 %Seneca County97.7Wyandot County: 97.6 %Wyandot County97.6Monroe County: 96.6 %Monroe County96.6Columbiana County: 94.1 %Columbiana County94.1Fayette County: 76.9 %Fayette County76.9Crawford County: 74.7 %Crawford County74.7Allen County: 71 %Allen County71Wood County: 69.6 %Wood County69.6Ashtabula County: 65.4 %Ashtabula County65.4Washington County: 65.2 %Washington County65.2Noble County: 64.2 %Noble County64.2Warren County: 64 %Warren County64Licking County: 62.9 %Licking County62.9Lake County: 62.5 %Lake County62.5Greene County: 62 %Greene County62Medina County: 60.3 %Medina County60.3Clermont County: 60.1 %Clermont County60.1Knox County: 59.8 %Knox County59.8Madison County: 57.9 %Madison County57.9Lorain County: 57.4 %Lorain County57.4Miami County: 56.5 %Miami County56.5Geauga County: 55.6 %Geauga County55.6Scioto County: 55.2 %Scioto County55.2Delaware County: 54.9 %Delaware County54.9Clinton County: 54.2 %Clinton County54.2Stark County: 54.2 %Stark County54.2Preble County: 53.7 %Preble County53.7Portage County: 46.4 %Portage County46.4Athens County: 43 %Athens County43Clark County: 42.1 %Clark County42.1Lawrence County: 39.9 %Lawrence County39.9Lucas County: 22.2 %Lucas County22.2Trumbull County: 20.9 %Trumbull County20.9Montgomery County: 20.3 %Montgomery County20.3Mahoning County: 20.1 %Mahoning County20.1Butler County: 18.9 %Butler County18.9Jefferson County: 17.5 %Jefferson County17.5Summit County: 17.5 %Summit County17.5Franklin County: 15.9 %Franklin County15.9Cuyahoga County: 12.9 %Cuyahoga County12.9Hamilton County: 11.2 %Hamilton County11.2
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2001 (%)Change on 2000
1Hancock County1000 pts
1Ottawa County1000 pts
1Sandusky County100+1.6 pts
4Belmont County98.3+6.8 pts
5Seneca County97.7-0.1 pts
6Wyandot County97.60 pts
7Monroe County96.6-3.4 pts
8Columbiana County94.1+13.2 pts
9Fayette County76.9+3.2 pts
10Crawford County74.7-6.6 pts
11Allen County71-6.9 pts
12Wood County69.6-5.3 pts
13Ashtabula County65.4+0.3 pts
14Washington County65.2-5.3 pts
15Noble County64.2-7.2 pts
16Warren County64-2.7 pts
17Licking County62.9-3.2 pts
18Lake County62.5-4.4 pts
19Greene County62-10.5 pts
20Medina County60.3-12.9 pts
21Clermont County60.1+0.9 pts
22Knox County59.8-4.7 pts
23Madison County57.9-0.3 pts
24Lorain County57.4-8.1 pts
25Miami County56.5-7.5 pts
26Geauga County55.6-12.5 pts
27Scioto County55.2-22.5 pts
28Delaware County54.9-14.3 pts
29Clinton County54.2+1.9 pts
29Stark County54.2-2 pts
31Preble County53.7+0.5 pts
32Portage County46.4-0.3 pts
33Athens County43+2.2 pts
34Clark County42.1-5.8 pts
35Lawrence County39.9-1 pts
36Lucas County22.2-17.3 pts
37Trumbull County20.9-3 pts
38Montgomery County20.3+2.8 pts
39Mahoning County20.1-2.2 pts
40Butler County18.9-4.3 pts
41Jefferson County17.5-5.2 pts
41Summit County17.5-0.8 pts
43Franklin County15.9-0.5 pts
44Cuyahoga County12.9+0.1 pts
45Hamilton County11.2+0.5 pts

Other periods

About this ranking

Days with a daily Air Quality Index of 0 to 50 (good) as a percentage of the days of the year with an AQI in a US county. Calculated by Invokely from the day counts in the EPA AirData annual summaries; both counts are stored with each value.

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: good days as a share of days with an AQI, calculated with stored counts. 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: good days as a share of days with an AQI, calculated with stored counts (Counties in Ohio by share of days with good air quality (US EPA AQI), 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: good days as a share of days with an AQI, calculated with stored counts, Counties in Ohio by share of days with good air quality (US EPA AQI), 2001. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/good-air-quality-days-share/ohio-counties. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. Counties in Ohio by share of days with good air quality (US EPA AQI), 2001. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/good-air-quality-days-share/ohio-counties.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts, Counties in Ohio by share of days with good air quality (US EPA AQI), 2001 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/good-air-quality-days-share/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: good days as a share of days with an AQI, calculated with stored counts: Counties in Ohio by share of days with good air quality (US EPA AQI), 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/good-air-quality-days-share/ohio-counties. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. 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: good days as a share of days with an AQI, calculated with stored counts: Counties in Ohio by share of days with good air quality (US EPA AQI), 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/good-air-quality-days-share/ohio-counties
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/ohio-counties.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. 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 share of days with good air quality (US EPA AQI)?

Hancock County, with 100% in 2001, according to EPA.

Which county has the lowest share of days with good air quality (US EPA AQI)?

Hamilton County, with 11.2% 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: good days as a share of days with an AQI, calculated with stored counts. Retrieved 2026-10-12. 13 counties have no value for 2001 and are not ranked.

Share of days with good air quality (US EPA AQI): other rankings

Counties in Ohio: more rankings