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

Douglas County had the highest share of days with good air quality (US EPA AQI) of 34 counties in 2004, at 100%. Grant County had the lowest, at 50%. The median was 84.1%. Source: EPA.

Highest100Douglas County

Lowest50Grant County

Median84.134 counties

Map of counties, 2004

Under 68
68 to 79
79 to 84
84 to 87
87 to 90
90 and over
No data

%, 2004. 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, 2004

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

Full ranking

Rank	Counties	2004 (%)	Change on 2003
1	Douglas County	100	+14.3 pts
1	Eau Claire County	100	0 pts
3	Ashland County	93.2	+9.3 pts
4	Forest County	92.8	-5.4 pts
5	Florence County	91.2	+8.1 pts
6	Green County	90.9	+27.3 pts
7	Oneida County	89.8	+14.7 pts
8	Marathon County	89.1	+16.6 pts
9	Vernon County	88.5	+27.4 pts
10	Columbia County	88	+25.5 pts
11	Fond du Lac County	87.4	+15.1 pts
12	Vilas County	86.7	+6.4 pts
13	Kewaunee County	84.8	+10.3 pts
14	Racine County	84.6	+6.6 pts
14	Washington County	84.6	+10.1 pts
16	Jefferson County	84.4	+22.6 pts
17	Taylor County	84.2	+6.4 pts
18	St. Croix County	84	+12.3 pts
19	Rock County	82.8	+21 pts
20	Sheboygan County	82.6	+14.7 pts
21	Walworth County	79.3	+19.7 pts
22	Sauk County	79.1	+4 pts
23	Door County	78.9	+2.1 pts
24	Manitowoc County	74.2	+9.2 pts
25	Ozaukee County	71.7	+6.9 pts
26	Outagamie County	71.3	+3 pts
27	Brown County	69	+5.3 pts
28	Milwaukee County	68.9	+5.3 pts
29	Waukesha County	67.7	+17.4 pts
30	Dane County	67.6	+12.9 pts
31	Waupaca County	62.5	n/a
32	Kenosha County	62.3	+5 pts
33	Dodge County	53.7	+0.3 pts
34	Grant County	50	+2.1 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. 14 counties with data in other periods have no value for 2004 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), 2004) [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), 2004. 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=2004. 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), 2004. 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=2004.

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), 2004 [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=2004 (Accessed: 12 October 2026).

BibTeX

@misc{environmental_counties_in_wisconsin_by_2004,
  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), 2004}},
  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=2004. 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), 2004
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=2004
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/wisconsin-counties?period=2004.
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)?

Douglas County, with 100% in 2004, according to EPA.

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

Grant County, with 50% in 2004.

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. 14 counties have no value for 2004 and are not ranked.