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 46 counties in 2000, at 100%. Hamilton County had the lowest, at 10.7%. The median was 65.8%. Source: EPA.

Highest100Hancock County

Lowest10.7Hamilton County

Median65.846 counties

Map of counties, 2000

Under 24
24 to 53
53 to 66
66 to 73
73 to 86
86 and over
No data

%, 2000. 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, 2000

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

Full ranking

Rank	Counties	2000 (%)	Change on 1999
1	Hancock County	100	0 pts
1	Monroe County	100	+1.7 pts
1	Ottawa County	100	+3.6 pts
1	Richland County	100	+0.6 pts
5	Sandusky County	98.4	+12.2 pts
6	Seneca County	97.8	+6.6 pts
7	Wyandot County	97.6	-0.6 pts
8	Belmont County	91.5	-3.4 pts
9	Crawford County	81.3	+9 pts
10	Columbiana County	80.9	+14.8 pts
11	Allen County	77.9	+13.8 pts
12	Scioto County	77.7	+12.6 pts
13	Wood County	74.9	+9.5 pts
14	Fayette County	73.7	+12.5 pts
15	Medina County	73.2	+7.5 pts
16	Greene County	72.5	+14.9 pts
17	Noble County	71.4	+0.7 pts
18	Washington County	70.5	+6.8 pts
19	Delaware County	69.2	+12.7 pts
20	Geauga County	68.1	+9.1 pts
21	Lake County	66.9	+9.6 pts
22	Warren County	66.7	+20 pts
23	Licking County	66.1	+12.2 pts
24	Lorain County	65.5	+6.1 pts
25	Ashtabula County	65.1	+4.5 pts
26	Knox County	64.5	+6.6 pts
27	Miami County	64	+5.3 pts
28	Clermont County	59.2	+17.2 pts
29	Madison County	58.2	+10.1 pts
30	Stark County	56.2	+4.7 pts
31	Preble County	53.2	+6.6 pts
32	Clinton County	52.3	+12.1 pts
33	Clark County	47.9	-4.9 pts
34	Portage County	46.7	+7.9 pts
35	Lawrence County	40.9	-3.1 pts
36	Athens County	40.8	+11.2 pts
37	Lucas County	39.5	-1.9 pts
38	Trumbull County	23.9	+3.7 pts
39	Butler County	23.2	+0.6 pts
40	Jefferson County	22.7	-7.4 pts
41	Mahoning County	22.3	+5.6 pts
42	Summit County	18.3	+3.2 pts
43	Montgomery County	17.5	-2.2 pts
44	Franklin County	16.4	+4.1 pts
45	Cuyahoga County	12.8	-0.6 pts
46	Hamilton County	10.7	-4.1 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. 12 counties with data in other periods have no value for 2000 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), 2000) [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), 2000. 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=2000. 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), 2000. 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=2000.

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), 2000 [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=2000 (Accessed: 12 October 2026).

BibTeX

@misc{environmental_counties_in_ohio_by_2000,
  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), 2000}},
  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=2000. 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), 2000
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=2000
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/ohio-counties?period=2000.
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 2000, according to EPA.

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

Hamilton County, with 10.7% in 2000.

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. 12 counties have no value for 2000 and are not ranked.