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

Sheboygan County had the highest highest daily Air Quality Index (US EPA) of 32 counties in 2000, at 200. Douglas County had the lowest, at 90. The median was 150. Source: the U.S. Environmental Protection Agency.

Highest200Sheboygan County

Lowest90Douglas County

Median15032 counties

Map of counties, 2000

Under 120
120 to 140
140 to 150
150 to 160
160 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	Sheboygan County	200	0
2	Manitowoc County	197	+7
3	Door County	177	-31
4	Rock County	172	-7
5	Jefferson County	164	-31
5	Ozaukee County	164	-28
7	Kenosha County	159	-36
8	Green County	156	n/a
8	Kewaunee County	156	-36
8	Milwaukee County	156	-41
11	Brown County	154	-18
11	Dodge County	154	-18
11	Racine County	154	-31
14	Columbia County	151	-21
14	Waukesha County	151	-41
16	Fond du Lac County	150	-29
16	Marathon County	150	-16
18	Sauk County	147	-38
18	Washington County	147	-30
18	Winnebago County	147	-22
21	Walworth County	143	-62
22	Outagamie County	136	-46
23	Taylor County	133	-44
23	Vernon County	133	-41
25	Dane County	122	-52
25	Florence County	122	-39
25	St. Croix County	122	-11
25	Vilas County	122	-32
29	Oneida County	115	-46
30	Grant County	113	-2
31	Wood County	111	0
32	Douglas County	90	0

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. 16 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 Wisconsin 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 Wisconsin 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/wisconsin-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 Wisconsin 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/wisconsin-counties?period=2000.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: highest daily AQI, Counties in Wisconsin 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/wisconsin-counties?period=2000 (Accessed: 12 October 2026).

BibTeX

@misc{environmental_counties_in_wisconsin_by_2000,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: highest daily AQI: Counties in Wisconsin 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/wisconsin-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 Wisconsin 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/wisconsin-counties?period=2000
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/highest-daily-air-quality-index/wisconsin-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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rank_places {"indicator":"aqi_max","level":"province","within":"Wisconsin","limit":10}
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Questions

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

Sheboygan County, with 200 in 2000, according to the U.S. Environmental Protection Agency.

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

Douglas County, with 90 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. 16 counties have no value for 2000 and are not ranked.