Data / Rankings / Share of days with good air quality (US EPA AQI) / Counties in Wisconsin

Counties in Wisconsin by share of days with good air quality (US EPA AQI)

Polk County had the highest share of days with good air quality (US EPA AQI) of 32 counties in 1999, at 100%. Milwaukee County had the lowest, at 27.7%. The median was 68.8%. Source: EPA.

Keep it in a collection in your library.
Highest100Polk County
Lowest27.7Milwaukee County
Median68.832 counties

Map of counties, 1999

Brown County: 60.7 %Columbia County: 70.5 %Dane County: 60.9 %Dodge County: 57.4 %Door County: 70.6 %Douglas County: 70.5 %Florence County: 81.9 %Fond du Lac County: 70.7 %Grant County: 35.1 %Jefferson County: 45.6 %Kenosha County: 51.5 %Kewaunee County: 71 %Manitowoc County: 62.9 %Marathon County: 74.8 %Milwaukee County: 27.7 %Oneida County: 82.2 %Outagamie County: 62.9 %Ozaukee County: 54.4 %Polk County: 100 %Racine County: 84.6 %Rock County: 46.1 %St. Croix County: 72.1 %Sauk County: 78 %Sheboygan County: 69.1 %Taylor County: 84.3 %Vernon County: 77.3 %Vilas County: 83.9 %Walworth County: 62.2 %Washington County: 68.5 %Waukesha County: 66 %Winnebago County: 57.6 %Wood County: 49.1 %
  • Under 52
  • 52 to 61
  • 61 to 69
  • 69 to 71
  • 71 to 81
  • 81 and over
  • No data
%, 1999. 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, 1999

Polk County: 100 %Polk County100Racine County: 84.6 %Racine County84.6Taylor County: 84.3 %Taylor County84.3Vilas County: 83.9 %Vilas County83.9Oneida County: 82.2 %Oneida County82.2Florence County: 81.9 %Florence County81.9Sauk County: 78 %Sauk County78Vernon County: 77.3 %Vernon County77.3Marathon County: 74.8 %Marathon County74.8St. Croix County: 72.1 %St. Croix County72.1Kewaunee County: 71 %Kewaunee County71Fond du Lac County: 70.7 %Fond du Lac County70.7Door County: 70.6 %Door County70.6Columbia County: 70.5 %Columbia County70.5Douglas County: 70.5 %Douglas County70.5Sheboygan County: 69.1 %Sheboygan County69.1Washington County: 68.5 %Washington County68.5Waukesha County: 66 %Waukesha County66Manitowoc County: 62.9 %Manitowoc County62.9Outagamie County: 62.9 %Outagamie County62.9Walworth County: 62.2 %Walworth County62.2Dane County: 60.9 %Dane County60.9Brown County: 60.7 %Brown County60.7Winnebago County: 57.6 %Winnebago County57.6Dodge County: 57.4 %Dodge County57.4Ozaukee County: 54.4 %Ozaukee County54.4Kenosha County: 51.5 %Kenosha County51.5Wood County: 49.1 %Wood County49.1Rock County: 46.1 %Rock County46.1Jefferson County: 45.6 %Jefferson County45.6Grant County: 35.1 %Grant County35.1Milwaukee County: 27.7 %Milwaukee County27.7Polk County: 100 %Polk County100Racine County: 84.6 %Racine County84.6Taylor County: 84.3 %Taylor County84.3Vilas County: 83.9 %Vilas County83.9Oneida County: 82.2 %Oneida County82.2Florence County: 81.9 %Florence County81.9Sauk County: 78 %Sauk County78Vernon County: 77.3 %Vernon County77.3Marathon County: 74.8 %Marathon County74.8St. Croix County: 72.1 %St. Croix County72.1Kewaunee County: 71 %Kewaunee County71Fond du Lac County: 70.7 %Fond du Lac County70.7Door County: 70.6 %Door County70.6Columbia County: 70.5 %Columbia County70.5Douglas County: 70.5 %Douglas County70.5Sheboygan County: 69.1 %Sheboygan County69.1Washington County: 68.5 %Washington County68.5Waukesha County: 66 %Waukesha County66Manitowoc County: 62.9 %Manitowoc County62.9Outagamie County: 62.9 %Outagamie County62.9Walworth County: 62.2 %Walworth County62.2Dane County: 60.9 %Dane County60.9Brown County: 60.7 %Brown County60.7Winnebago County: 57.6 %Winnebago County57.6Dodge County: 57.4 %Dodge County57.4Ozaukee County: 54.4 %Ozaukee County54.4Kenosha County: 51.5 %Kenosha County51.5Wood County: 49.1 %Wood County49.1Rock County: 46.1 %Rock County46.1Jefferson County: 45.6 %Jefferson County45.6Grant County: 35.1 %Grant County35.1Milwaukee County: 27.7 %Milwaukee County27.7
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties1999 (%)Change on 1998
1Polk County100+11.5 pts
2Racine County84.6+3.8 pts
3Taylor County84.3-2 pts
4Vilas County83.9-7.1 pts
5Oneida County82.2+0.5 pts
6Florence County81.9+2.6 pts
7Sauk County78-3.6 pts
8Vernon County77.3+0.2 pts
9Marathon County74.8+2 pts
10St. Croix County72.1-5.7 pts
11Kewaunee County71+4.2 pts
12Fond du Lac County70.7+8.2 pts
13Door County70.6+4.5 pts
14Columbia County70.5+2.7 pts
14Douglas County70.5-29.5 pts
16Sheboygan County69.1-1 pts
17Washington County68.5+0.9 pts
18Waukesha County66-12.2 pts
19Manitowoc County62.9+3.7 pts
19Outagamie County62.9-13.7 pts
21Walworth County62.2-1.3 pts
22Dane County60.9-16.2 pts
23Brown County60.7-15.8 pts
24Winnebago County57.6-14.2 pts
25Dodge County57.4-4.6 pts
26Ozaukee County54.4-1 pts
27Kenosha County51.5+12.6 pts
28Wood County49.1n/a
29Rock County46.1-8.8 pts
30Jefferson County45.6-16.4 pts
31Grant County35.1n/a
32Milwaukee County27.7-39.4 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. 16 counties with data in other periods have no value for 1999 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 Wisconsin by share of days with good air quality (US EPA AQI), 1999) [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 Wisconsin by share of days with good air quality (US EPA AQI), 1999. 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/wisconsin-counties?period=1999. 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 Wisconsin by share of days with good air quality (US EPA AQI), 1999. 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/wisconsin-counties?period=1999.

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 Wisconsin by share of days with good air quality (US EPA AQI), 1999 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/good-air-quality-days-share/wisconsin-counties?period=1999 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_wisconsin_by_1999,
  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 Wisconsin by share of days with good air quality (US EPA AQI), 1999}},
  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/wisconsin-counties?period=1999. 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 Wisconsin by share of days with good air quality (US EPA AQI), 1999
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/wisconsin-counties?period=1999
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/wisconsin-counties?period=1999.
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  -
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.

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 share of days with good air quality (US EPA AQI) using official data, and cite the source.
rank_places {"indicator":"aqi_good_days_share","level":"province","within":"Wisconsin","limit":10}
GET https://invokely.ai/api/v1/rank?indicator=aqi_good_days_share&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 share of days with good air quality (US EPA AQI)?

Polk County, with 100% in 1999, according to EPA.

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

Milwaukee County, with 27.7% in 1999.

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. 16 counties have no value for 1999 and are not ranked.

Share of days with good air quality (US EPA AQI): other rankings

Counties in Wisconsin: more rankings