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

Clinton County had the highest highest daily Air Quality Index (US EPA) of 45 counties in 2001, at 203. Sandusky County had the lowest, at 36. The median was 174. Source: the U.S. Environmental Protection Agency.

Highest203Clinton County

Lowest36Sandusky County

Median17445 counties

Map of counties, 2001

Under 77
77 to 160
160 to 170
170 to 190
190 to 200
200 and over
No data

index, 2001. Hatched areas have no value for this period. Source: EPA, EPA AirData annual AQI by county: highest daily AQI. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2001

index. Source: EPA, EPA AirData annual AQI by county: highest daily AQI. Retrieved 2026-10-12.

Full ranking

Rank	Counties	2001 index	Change on 2000
1	Clinton County	203	-2
1	Summit County	203	+18
3	Jefferson County	202	+25
3	Mahoning County	202	+17
5	Ashtabula County	200	-1
5	Hamilton County	200	+13
7	Butler County	195	0
7	Medina County	195	+13
7	Portage County	195	+13
10	Geauga County	192	+2
10	Madison County	192	-11
12	Lake County	190	+3
12	Lucas County	190	+34
12	Trumbull County	190	0
15	Franklin County	187	+8
15	Stark County	187	-3
17	Cuyahoga County	185	+11
18	Knox County	179	-28
19	Delaware County	177	0
19	Miami County	177	-15
21	Fayette County	174	-27
21	Lawrence County	174	+10
21	Noble County	174	+2
21	Washington County	174	-5
25	Montgomery County	172	-20
26	Licking County	169	-32
26	Warren County	169	-31
26	Wood County	169	+18
29	Clark County	166	-43
30	Clermont County	164	-23
31	Crawford County	161	-34
31	Greene County	161	-40
31	Lorain County	161	-21
34	Scioto County	160	+9
35	Allen County	159	-18
36	Preble County	136	-28
37	Athens County	114	+20
38	Wyandot County	58	-6
39	Seneca County	56	-21
40	Monroe County	54	+4
41	Belmont County	53	-6
41	Columbiana County	53	-35
43	Ottawa County	40	-4
44	Hancock County	38	-6
45	Sandusky County	36	-15

Other periods

About this ranking

Highest daily Air Quality Index (AQI) value recorded in a US county during the year, from the EPA AirData annual summaries. Values above 500 are beyond the AQI scale and are published as EPA computes them.

A single day decides the value, so one wildfire or dust event can set it. Dust from the dry Owens Lake bed puts Inyo and Mono counties in California in the thousands. 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: highest 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: highest daily AQI (Counties in Ohio by highest daily 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: highest daily AQI, Counties in Ohio by highest daily 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/highest-daily-air-quality-index/ohio-counties. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: highest daily AQI. Counties in Ohio by highest daily 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/highest-daily-air-quality-index/ohio-counties.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: highest daily AQI, Counties in Ohio by highest daily 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/highest-daily-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: highest daily AQI: Counties in Ohio by highest daily 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/highest-daily-air-quality-index/ohio-counties. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: highest 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: highest daily AQI: Counties in Ohio by highest daily 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/highest-daily-air-quality-index/ohio-counties
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/highest-daily-air-quality-index/ohio-counties.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: highest daily AQI. 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 highest daily Air Quality Index (US EPA)?

Clinton County, with 203 in 2001, according to the U.S. Environmental Protection Agency.

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

Sandusky County, with 36 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: highest daily AQI. Retrieved 2026-10-12. 13 counties have no value for 2001 and are not ranked.