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

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

Allegan County had the highest median Air Quality Index (US EPA) of 33 counties in 1991, at 80. Gratiot County had the lowest, at 5. The median was 35. Source: the U.S. Environmental Protection Agency.

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Highest80Allegan County
Lowest5Gratiot County
Median3533 counties

Map of counties, 1991

Allegan County: 80 indexBay County: 20 indexBenzie County: 44 indexBerrien County: 80 indexCalhoun County: 21 indexCass County: 71 indexClinton County: 42 indexDelta County: 41 indexDickinson County: 32 indexGenesee County: 39 indexGratiot County: 5 indexHoughton County: 34 indexIngham County: 40 indexKalamazoo County: 29 indexKent County: 31 indexKeweenaw County: 23 indexMacomb County: 30 indexManistee County: 34 indexMarquette County: 12 indexMason County: 42 indexMidland County: 19 indexMonroe County: 22 indexMontcalm County: 51 indexMuskegon County: 43 indexOakland County: 25 indexOceana County: 51 indexOttawa County: 44 indexSaginaw County: 25 indexSt. Clair County: 40 indexTuscola County: 36 indexVan Buren County: 30 indexWashtenaw County: 35 indexWayne County: 44 index
  • Under 22
  • 22 to 30
  • 30 to 35
  • 35 to 41
  • 41 to 44
  • 44 and over
  • No data
index, 1991. 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, 1991

Allegan County: 80 indexAllegan County80Berrien County: 80 indexBerrien County80Cass County: 71 indexCass County71Montcalm County: 51 indexMontcalm County51Oceana County: 51 indexOceana County51Benzie County: 44 indexBenzie County44Ottawa County: 44 indexOttawa County44Wayne County: 44 indexWayne County44Muskegon County: 43 indexMuskegon County43Clinton County: 42 indexClinton County42Mason County: 42 indexMason County42Delta County: 41 indexDelta County41Ingham County: 40 indexIngham County40St. Clair County: 40 indexSt. Clair County40Genesee County: 39 indexGenesee County39Tuscola County: 36 indexTuscola County36Washtenaw County: 35 indexWashtenaw County35Houghton County: 34 indexHoughton County34Manistee County: 34 indexManistee County34Dickinson County: 32 indexDickinson County32Kent County: 31 indexKent County31Macomb County: 30 indexMacomb County30Van Buren County: 30 indexVan Buren County30Kalamazoo County: 29 indexKalamazoo County29Oakland County: 25 indexOakland County25Saginaw County: 25 indexSaginaw County25Keweenaw County: 23 indexKeweenaw County23Monroe County: 22 indexMonroe County22Calhoun County: 21 indexCalhoun County21Bay County: 20 indexBay County20Midland County: 19 indexMidland County19Marquette County: 12 indexMarquette County12Gratiot County: 5 indexGratiot County5Allegan County: 80 indexAllegan County80Berrien County: 80 indexBerrien County80Cass County: 71 indexCass County71Montcalm County: 51 indexMontcalm County51Oceana County: 51 indexOceana County51Benzie County: 44 indexBenzie County44Ottawa County: 44 indexOttawa County44Wayne County: 44 indexWayne County44Muskegon County: 43 indexMuskegon County43Clinton County: 42 indexClinton County42Mason County: 42 indexMason County42Delta County: 41 indexDelta County41Ingham County: 40 indexIngham County40St. Clair County: 40 indexSt. Clair County40Genesee County: 39 indexGenesee County39Tuscola County: 36 indexTuscola County36Washtenaw County: 35 indexWashtenaw County35Houghton County: 34 indexHoughton County34Manistee County: 34 indexManistee County34Dickinson County: 32 indexDickinson County32Kent County: 31 indexKent County31Macomb County: 30 indexMacomb County30Van Buren County: 30 indexVan Buren County30Kalamazoo County: 29 indexKalamazoo County29Oakland County: 25 indexOakland County25Saginaw County: 25 indexSaginaw County25Keweenaw County: 23 indexKeweenaw County23Monroe County: 22 indexMonroe County22Calhoun County: 21 indexCalhoun County21Bay County: 20 indexBay County20Midland County: 19 indexMidland County19Marquette County: 12 indexMarquette County12Gratiot County: 5 indexGratiot County5
index. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Retrieved 2026-10-12.

Full ranking

RankCounties1991
index		Change on 1990
1Allegan County80+29
1Berrien County80n/a
3Cass County71n/a
4Montcalm County51n/a
4Oceana County51n/a
6Benzie County44n/a
6Ottawa County44+3
6Wayne County44-3
9Muskegon County430
10Clinton County420
10Mason County42+19
12Delta County41n/a
13Ingham County40+1
13St. Clair County400
15Genesee County39-1
16Tuscola County36-1
17Washtenaw County35-1
18Houghton County34+2
18Manistee County340
20Dickinson County32-2
21Kent County310
22Macomb County300
22Van Buren County30n/a
24Kalamazoo County29n/a
25Oakland County250
25Saginaw County25+6
27Keweenaw County23-1
28Monroe County22-6
29Calhoun County21-3
30Bay County20-3
31Midland County190
32Marquette County12-1
33Gratiot County50

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. 20 counties with data in other periods have no value for 1991 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 Michigan by median Air Quality Index (US EPA), 1991) [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 Michigan by median Air Quality Index (US EPA), 1991. 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/michigan-counties?period=1991. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: median daily AQI. Counties in Michigan by median Air Quality Index (US EPA), 1991. 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/michigan-counties?period=1991.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: median daily AQI, Counties in Michigan by median Air Quality Index (US EPA), 1991 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/median-air-quality-index/michigan-counties?period=1991 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_michigan_by_1991,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: median daily AQI: Counties in Michigan by median Air Quality Index (US EPA), 1991}},
  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/michigan-counties?period=1991. 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 Michigan by median Air Quality Index (US EPA), 1991
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/michigan-counties?period=1991
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/median-air-quality-index/michigan-counties?period=1991.
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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Rank Counties in Michigan by median Air Quality Index (US EPA) using official data, and cite the source.
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Questions

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

Allegan County, with 80 in 1991, according to the U.S. Environmental Protection Agency.

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

Gratiot County, with 5 in 1991.

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. 20 counties have no value for 1991 and are not ranked.

Median Air Quality Index (US EPA): other rankings

Counties in Michigan: more rankings