Data / Rankings / Median Air Quality Index (US EPA) / Counties in Wisconsin

Counties in Wisconsin by median Air Quality Index (US EPA)

Waukesha County had the highest median Air Quality Index (US EPA) of 35 counties in 2002, at 53. Forest County had the lowest, at 10. The median was 43. Source: the U.S. Environmental Protection Agency.

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Highest53Waukesha County
Lowest10Forest County
Median4335 counties

Map of counties, 2002

Ashland County: 17 indexBrown County: 43 indexColumbia County: 44 indexDane County: 48 indexDodge County: 43 indexDoor County: 41 indexDouglas County: 38 indexEau Claire County: 13 indexFlorence County: 38 indexFond du Lac County: 43 indexForest County: 10 indexGrant County: 52 indexGreen County: 44 indexJefferson County: 48 indexKenosha County: 48 indexKewaunee County: 42 indexManitowoc County: 43 indexMarathon County: 42 indexMilwaukee County: 49 indexOneida County: 37 indexOutagamie County: 42 indexOzaukee County: 45 indexRacine County: 21 indexRock County: 48 indexSt. Croix County: 42 indexSauk County: 37 indexSheboygan County: 44 indexTaylor County: 36 indexVernon County: 43 indexVilas County: 32 indexWalworth County: 46 indexWashington County: 44 indexWaukesha County: 53 indexWinnebago County: 44 indexWood County: 51 index
  • Under 37
  • 37 to 42
  • 42 to 43
  • 43 to 44
  • 44 to 48
  • 48 and over
  • No data
index, 2002. Hatched areas have no value for this period. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2002

Waukesha County: 53 indexWaukesha County53Grant County: 52 indexGrant County52Wood County: 51 indexWood County51Milwaukee County: 49 indexMilwaukee County49Dane County: 48 indexDane County48Jefferson County: 48 indexJefferson County48Kenosha County: 48 indexKenosha County48Rock County: 48 indexRock County48Walworth County: 46 indexWalworth County46Ozaukee County: 45 indexOzaukee County45Columbia County: 44 indexColumbia County44Green County: 44 indexGreen County44Sheboygan County: 44 indexSheboygan County44Washington County: 44 indexWashington County44Winnebago County: 44 indexWinnebago County44Brown County: 43 indexBrown County43Dodge County: 43 indexDodge County43Fond du Lac County: 43 indexFond du Lac County43Manitowoc County: 43 indexManitowoc County43Vernon County: 43 indexVernon County43Kewaunee County: 42 indexKewaunee County42Marathon County: 42 indexMarathon County42Outagamie County: 42 indexOutagamie County42St. Croix County: 42 indexSt. Croix County42Door County: 41 indexDoor County41Douglas County: 38 indexDouglas County38Florence County: 38 indexFlorence County38Oneida County: 37 indexOneida County37Sauk County: 37 indexSauk County37Taylor County: 36 indexTaylor County36Vilas County: 32 indexVilas County32Racine County: 21 indexRacine County21Ashland County: 17 indexAshland County17Eau Claire County: 13 indexEau Claire County13Forest County: 10 indexForest County10Waukesha County: 53 indexWaukesha County53Grant County: 52 indexGrant County52Wood County: 51 indexWood County51Milwaukee County: 49 indexMilwaukee County49Dane County: 48 indexDane County48Jefferson County: 48 indexJefferson County48Kenosha County: 48 indexKenosha County48Rock County: 48 indexRock County48Walworth County: 46 indexWalworth County46Ozaukee County: 45 indexOzaukee County45Columbia County: 44 indexColumbia County44Green County: 44 indexGreen County44Sheboygan County: 44 indexSheboygan County44Washington County: 44 indexWashington County44Winnebago County: 44 indexWinnebago County44Brown County: 43 indexBrown County43Dodge County: 43 indexDodge County43Fond du Lac County: 43 indexFond du Lac County43Manitowoc County: 43 indexManitowoc County43Vernon County: 43 indexVernon County43Kewaunee County: 42 indexKewaunee County42Marathon County: 42 indexMarathon County42Outagamie County: 42 indexOutagamie County42St. Croix County: 42 indexSt. Croix County42Door County: 41 indexDoor County41Douglas County: 38 indexDouglas County38Florence County: 38 indexFlorence County38Oneida County: 37 indexOneida County37Sauk County: 37 indexSauk County37Taylor County: 36 indexTaylor County36Vilas County: 32 indexVilas County32Racine County: 21 indexRacine County21Ashland County: 17 indexAshland County17Eau Claire County: 13 indexEau Claire County13Forest County: 10 indexForest County10
index. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Retrieved 2026-10-12.

Full ranking

RankCounties2002
index		Change on 2001
1Waukesha County53-3
2Grant County520
3Wood County51+7
4Milwaukee County49-10
5Dane County48+5
5Jefferson County48+1
5Kenosha County48-4
5Rock County48-2
9Walworth County460
10Ozaukee County45-2
11Columbia County440
11Green County440
11Sheboygan County440
11Washington County44+2
11Winnebago County440
16Brown County43-1
16Dodge County43+2
16Fond du Lac County43+1
16Manitowoc County43-1
16Vernon County43+2
21Kewaunee County420
21Marathon County42+3
21Outagamie County42-1
21St. Croix County42+1
25Door County41-1
26Douglas County38-3
26Florence County38-1
28Oneida County37-3
28Sauk County37-6
30Taylor County36+1
31Vilas County32-4
32Racine County21+1
33Ashland County17+6
34Eau Claire County13n/a
35Forest County10n/a

Other periods

About this ranking

Median of the daily Air Quality Index (AQI) values of a US county over the days of the year with an AQI, from the EPA AirData annual summaries.

More on how it is measured
  • The daily county AQI is the highest AQI among the monitors and pollutants reported that day (ozone, PM2.5, PM10, carbon monoxide and nitrogen dioxide).
  • Lower is cleaner: 0 to 50 is good, 51 to 100 moderate and above 100 unhealthy for sensitive groups.

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. 13 counties with data in other periods have no value for 2002 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: median 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: median daily AQI (Counties in Wisconsin by median Air Quality Index (US EPA), 2002) [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: median daily AQI, Counties in Wisconsin by median Air Quality Index (US EPA), 2002. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/median-air-quality-index/wisconsin-counties?period=2002. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: median daily AQI. Counties in Wisconsin by median Air Quality Index (US EPA), 2002. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/median-air-quality-index/wisconsin-counties?period=2002.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: median daily AQI, Counties in Wisconsin by median Air Quality Index (US EPA), 2002 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/median-air-quality-index/wisconsin-counties?period=2002 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_wisconsin_by_2002,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: median daily AQI: Counties in Wisconsin by median Air Quality Index (US EPA), 2002}},
  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/median-air-quality-index/wisconsin-counties?period=2002. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median 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: median daily AQI: Counties in Wisconsin by median Air Quality Index (US EPA), 2002
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/median-air-quality-index/wisconsin-counties?period=2002
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/median-air-quality-index/wisconsin-counties?period=2002.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. 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 median Air Quality Index (US EPA)?

Waukesha County, with 53 in 2002, according to the U.S. Environmental Protection Agency.

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

Forest County, with 10 in 2002.

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: median daily AQI. Retrieved 2026-10-12. 13 counties have no value for 2002 and are not ranked.

Median Air Quality Index (US EPA): other rankings

Counties in Wisconsin: more rankings