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

Ozaukee County had the highest highest daily Air Quality Index (US EPA) of 33 counties in 2001, at 214. Ashland County had the lowest, at 40. The median was 161. Source: the U.S. Environmental Protection Agency.

Highest214Ozaukee County

Lowest40Ashland County

Median16133 counties

Map of counties, 2001

Under 120
120 to 160
160 to 170
170 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	Ozaukee County	214	+50
2	Sheboygan County	212	+12
3	Kenosha County	209	+50
4	Milwaukee County	208	+52
5	Door County	207	+30
6	Racine County	203	+49
7	Manitowoc County	202	+5
8	Walworth County	190	+47
9	Kewaunee County	187	+31
10	Brown County	185	+31
11	Jefferson County	174	+10
12	Florence County	172	+50
13	Dane County	164	+42
13	Taylor County	164	+31
13	Washington County	164	+17
16	Fond du Lac County	161	+11
16	Outagamie County	161	+25
16	Rock County	161	-11
16	Waukesha County	161	+10
16	Winnebago County	161	+14
21	Dodge County	159	+5
21	St. Croix County	159	+37
23	Columbia County	151	0
24	Green County	147	-9
25	Marathon County	126	-24
26	Oneida County	122	+7
26	Sauk County	122	-25
28	Grant County	119	+6
29	Vilas County	112	-10
30	Vernon County	108	-25
31	Wood County	93	-18
32	Douglas County	82	-8
33	Ashland County	40	n/a

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. 15 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 Wisconsin 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 Wisconsin 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/wisconsin-counties?period=2001. 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), 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/wisconsin-counties?period=2001.

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), 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/wisconsin-counties?period=2001 (Accessed: 12 October 2026).

BibTeX

@misc{environmental_counties_in_wisconsin_by_2001,
  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), 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/wisconsin-counties?period=2001. 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), 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/wisconsin-counties?period=2001
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/highest-daily-air-quality-index/wisconsin-counties?period=2001.
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  -

Embed this chart

Paste this code into a web page or a blog post. The chart shows the latest figures as they are published, with the source and a link back to this page.

Embed code

<iframe src="https://invokely.ai/embed/rankings/highest-daily-air-quality-index/wisconsin-counties?period=2001" width="760" height="500" title="Counties in Wisconsin by highest daily Air Quality Index (US EPA), 2001, chart from Invokely" loading="lazy" style="border:0;width:100%;max-width:760px" referrerpolicy="strict-origin-when-cross-origin"></iframe>

Sites that read oEmbed links, such as WordPress, can show the chart when you paste the link to this page.

Use this data in your AI agent

Invokely serves this figure to AI assistants through MCP and to code through a REST API, with the source and citation attached. Ask your assistant:

Rank Counties in Wisconsin by highest daily Air Quality Index (US EPA) using official data, and cite the source.

rank_places {"indicator":"aqi_max","level":"province","within":"Wisconsin","limit":10}
GET https://invokely.ai/api/v1/rank?indicator=aqi_max&level=province&within=Wisconsin&limit=10

Connect Claude, ChatGPT or Cursor in one step. The trial answers 25 calls a day without an account.

Questions

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

Ozaukee County, with 214 in 2001, according to the U.S. Environmental Protection Agency.

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

Ashland County, with 40 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. 15 counties have no value for 2001 and are not ranked.