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

Ashland County had the highest share of days with good air quality (US EPA AQI) of 32 counties in 2006, at 92.5%. Waupaca County had the lowest, at 40%. The median was 76.9%. Source: EPA.

Highest92.5Ashland County

Lowest40Waupaca County

Median76.932 counties

Map of counties, 2006

Under 64
64 to 71
71 to 77
77 to 80
80 to 83
83 and over
No data

%, 2006. 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, 2006

%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

Rank	Counties	2006 (%)	Change on 2005
1	Ashland County	92.5	+0.6 pts
2	Forest County	91.9	+7.9 pts
3	Florence County	89.4	+9.9 pts
4	Columbia County	85.9	+20 pts
4	Oneida County	85.9	+9.8 pts
6	Racine County	83.2	+12.4 pts
7	Washington County	81.1	+12.5 pts
8	Door County	80.6	+13.4 pts
8	Vilas County	80.6	+6.3 pts
10	Jefferson County	80	+17.3 pts
11	Kewaunee County	79.7	+7.8 pts
12	Rock County	79.5	+15.2 pts
13	Fond du Lac County	79.3	+12.6 pts
14	Marathon County	78.9	+2 pts
15	Vernon County	78.7	+3.3 pts
16	Taylor County	77	-0.4 pts
17	Sauk County	76.8	+6.7 pts
18	Sheboygan County	75.1	+5.8 pts
19	St. Croix County	74.4	+2.4 pts
20	Dodge County	72.1	+24.7 pts
21	Walworth County	72	+10.7 pts
22	Waukesha County	69.9	+9.8 pts
23	Manitowoc County	67.6	+6.9 pts
24	Dane County	65.6	+13.8 pts
25	Brown County	65	+5.2 pts
26	Outagamie County	64.1	+5.3 pts
27	Ozaukee County	64	+6.4 pts
28	Milwaukee County	61.5	+2.6 pts
29	Kenosha County	57.1	+8.1 pts
30	Grant County	42.2	-7 pts
31	La Crosse County	40.3	+40.3 pts
32	Waupaca County	40	-13.8 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 2006 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), 2006) [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), 2006. 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=2006. 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), 2006. 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=2006.

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), 2006 [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=2006 (Accessed: 12 October 2026).

BibTeX

@misc{environmental_counties_in_wisconsin_by_2006,
  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), 2006}},
  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=2006. 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), 2006
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=2006
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/wisconsin-counties?period=2006.
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  -

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Questions

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

Ashland County, with 92.5% in 2006, according to EPA.

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

Waupaca County, with 40% in 2006.

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 2006 and are not ranked.