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

Hancock County had the highest share of days with good air quality (US EPA AQI) of 49 counties in 1999, at 100%. Franklin County had the lowest, at 12.3%. The median was 57.9%. Source: EPA.

Highest100Hancock County

Lowest12.3Franklin County

Median57.949 counties

Map of counties, 1999

Under 30
30 to 47
47 to 58
58 to 64
64 to 84
84 and over
No data

%, 1999. Hatched areas have no value for this period. Source: Invokely calculation with data from EPA. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 1999

%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

Rank	Counties	1999 (%)	Change on 1998
1	Hancock County	100	0 pts
2	Richland County	99.4	+1.1 pts
3	Monroe County	98.3	0 pts
4	Wyandot County	98.2	+4.2 pts
5	Ottawa County	96.4	-1.7 pts
6	Belmont County	94.9	-5.1 pts
7	Seneca County	91.2	-6.7 pts
8	Sandusky County	86.2	+11.6 pts
9	Erie County	84.4	-1.3 pts
10	Logan County	75.6	+12.6 pts
11	Crawford County	72.3	+4.4 pts
12	Noble County	70.7	+9.3 pts
13	Columbiana County	66.1	-25.8 pts
14	Medina County	65.7	+10.3 pts
15	Wood County	65.4	+9.1 pts
16	Scioto County	65.1	-34.5 pts
17	Allen County	64.1	+9.7 pts
18	Washington County	63.7	+1.4 pts
19	Fayette County	61.2	-2 pts
20	Union County	60.8	+1.5 pts
21	Ashtabula County	60.6	-1.2 pts
22	Lorain County	59.4	-17.9 pts
23	Geauga County	59	-1.3 pts
24	Miami County	58.7	+4.9 pts
25	Knox County	57.9	-3.1 pts
26	Greene County	57.6	+4.7 pts
27	Lake County	57.3	-16.5 pts
28	Delaware County	56.5	+13.4 pts
29	Licking County	53.9	+10 pts
30	Clark County	52.8	+12.1 pts
31	Stark County	51.5	-17 pts
32	Madison County	48.1	+4.6 pts
33	Warren County	46.7	-0.2 pts
34	Preble County	46.6	-10.7 pts
35	Lawrence County	44	-12.7 pts
36	Clermont County	42	-5.4 pts
37	Lucas County	41.4	-35.3 pts
38	Clinton County	40.2	-3.3 pts
39	Portage County	38.8	-18.3 pts
40	Jefferson County	30.1	-57.6 pts
41	Athens County	29.6	-70.4 pts
42	Butler County	22.6	-41.2 pts
43	Trumbull County	20.2	-35.6 pts
44	Montgomery County	19.7	-52.4 pts
45	Mahoning County	16.7	-49.1 pts
46	Summit County	15.1	-56.4 pts
47	Hamilton County	14.8	-36.2 pts
48	Cuyahoga County	13.4	-41.7 pts
49	Franklin County	12.3	-57 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. 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: 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), 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: 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), 1999. 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?period=1999. 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), 1999. 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?period=1999.

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), 1999 [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?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: 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), 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/good-air-quality-days-share/ohio-counties?period=1999. 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), 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/good-air-quality-days-share/ohio-counties?period=1999
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/ohio-counties?period=1999.
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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rank_places {"indicator":"aqi_good_days_share","level":"province","within":"Ohio","limit":10}
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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 1999, according to EPA.

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

Franklin County, with 12.3% 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: good days as a share of days with an AQI, calculated with stored counts. Retrieved 2026-10-12. 9 counties have no value for 1999 and are not ranked.