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

Clark County had the highest highest daily Air Quality Index (US EPA) of 46 counties in 2000, at 209. Ottawa County had the lowest, at 44. The median was 182. Source: the U.S. Environmental Protection Agency.

Highest209Clark County

Lowest44Ottawa County

Median18246 counties

Map of counties, 2000

Under 83
83 to 170
170 to 180
180 to 190
190 to 200
200 and over
No data

index, 2000. 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, 2000

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

Full ranking

Rank	Counties	2000 index	Change on 1999
1	Clark County	209	+9
2	Knox County	207	+5
3	Clinton County	205	+10
4	Madison County	203	+16
5	Ashtabula County	201	+4
5	Fayette County	201	+11
5	Greene County	201	+24
5	Licking County	201	+14
9	Warren County	200	+5
10	Butler County	195	-26
10	Crawford County	195	+13
12	Miami County	192	-5
12	Montgomery County	192	-15
14	Geauga County	190	-12
14	Stark County	190	-17
14	Trumbull County	190	+8
17	Clermont County	187	-26
17	Hamilton County	187	-22
17	Lake County	187	-27
20	Mahoning County	185	+8
20	Summit County	185	+6
22	Lorain County	182	-25
22	Medina County	182	+8
22	Portage County	182	-26
25	Franklin County	179	-53
25	Washington County	179	-35
27	Allen County	177	-15
27	Delaware County	177	-49
27	Jefferson County	177	-13
30	Cuyahoga County	174	-18
31	Noble County	172	-32
32	Lawrence County	164	-31
32	Preble County	164	+10
34	Lucas County	156	-51
35	Scioto County	151	-12
35	Wood County	151	-26
37	Athens County	94	-33
38	Columbiana County	88	-22
39	Seneca County	77	-31
40	Wyandot County	64	-3
41	Belmont County	59	0
42	Sandusky County	51	-19
43	Monroe County	50	-3
43	Richland County	50	-5
45	Hancock County	44	+11
45	Ottawa County	44	-11

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. 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: 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), 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: highest daily AQI, Counties in Ohio by highest daily Air Quality Index (US EPA), 2000. 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?period=2000. 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), 2000. 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?period=2000.

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), 2000 [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?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: highest daily AQI: Counties in Ohio by highest daily Air Quality Index (US EPA), 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/highest-daily-air-quality-index/ohio-counties?period=2000. 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), 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/highest-daily-air-quality-index/ohio-counties?period=2000
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/highest-daily-air-quality-index/ohio-counties?period=2000.
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)?

Clark County, with 209 in 2000, according to the U.S. Environmental Protection Agency.

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

Ottawa County, with 44 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: highest daily AQI. Retrieved 2026-10-12. 12 counties have no value for 2000 and are not ranked.