Which county in Michigan has the best air quality?

Based on 2024 EPA AQS data, Keweenaw County had the best air quality in Michigan with a median AQI of 12 and 118 good-air days.

2024 monitoring year Public dataset EPA AQS

Michigan Air Quality Rankings

Compiled by PlainEnviro Editorial, Environmental Data Editorial Team · July 13, 2026

County-level AQI rollup using EPA Air Quality System monitor records. Refreshed as new EPA AQS data lands.

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County-by-county air quality data for Michigan based on EPA AQS annual AQI readings. Data covers 28 monitored counties for 2024.

Michigan (2024): 28 counties monitored. State average median AQI: 38 (national average: 38.8). 78% of monitored days rated "Good." Most unhealthy air: Wayne County (1 days above AQI 100).

Michigan air quality on this page is drawn from the EPA Air Quality System (AQS), which aggregates daily readings from federal, state, tribal, and local monitors into annual summaries per county. The current dataset covers 28 Michigan counties with at least ten days of valid AQI readings in 2024, out of the state's total monitored counties.

The state-average median AQI across those counties is 38, compared with a national average of 38.8 in the same reporting period. On average, 78% of monitored days fell into the "Good" AQI bucket (0–50). The heaviest burden of unhealthy days lands on Wayne County (1 day above AQI 100), while Keweenaw County records the cleanest air with a median AQI of 12.

AQI values translate ambient concentrations of pollutants (ozone, PM2.5, PM10, NO₂, SO₂, CO) onto a single 0–500 scale with six health-based bands. A low median AQI reflects typical daily conditions; peak values matter separately because short-term exposure drives most acute health effects. Counties without monitors are not "clean" - they are simply unmeasured by EPA AQS. For site-specific exposure guidance, check AirNow.gov alongside the county detail links below.

Counties with Data

State Avg Median AQI

National Avg Median AQI

38.8

Avg Good Days %

78%

Which Michigan counties have the worst air quality?

Ranked by median AQI (higher = worse). Click a county for full environmental data.

#	County	Median AQI	Good Days	Good %	Unhealthy Days	Peak AQI
1	Wayne	55	120	33%	1	181
2	Kent	51	180	49%	0	112
3	Allegan	46	222	63%	0	115
4	Oakland	45	181	60%	0	101
5	Kalamazoo	45	234	64%	0	100
6	Washtenaw	43	253	69%	0	87
7	Lenawee	43	253	69%	0	97
8	Macomb	42	259	71%	0	115
9	Genesee	42	252	73%	0	119
10	Cass	42	205	82%	0	108
11	St. Clair	41	261	73%	0	134
12	Berrien	41	200	83%	0	101
13	Ottawa	41	257	70%	0	105
14	Ingham	39	281	77%	0	85
15	Huron	38	216	88%	0	119
16	Clinton	38	228	93%	0	80
17	Muskegon	38	203	84%	0	122
18	Benzie	38	216	88%	0	101
19	Bay	37	277	76%	0	73
20	Mason	37	218	89%	0	97
21	Missaukee	35	337	92%	0	84
22	Tuscola	34	331	91%	0	84
23	Wexford	34	341	94%	0	80
24	Manistee	33	125	81%	0	105
25	Schoolcraft	33	317	88%	0	93
26	Marquette	19	202	90%	0	67
27	Monroe	18	56	95%	0	77
28	Keweenaw	12	118	98%	0	66

Frequently Asked Questions

What is the air quality like in Michigan?

In 2024, Michigan had an average median AQI of 38 across 28 monitored counties, with 78% of monitored days rated "Good" (AQI 0–50). The national average median AQI is 38.8.

Which county in Michigan has the worst air quality?

Based on 2024 EPA AQS data, Wayne County had the most unhealthy air days in Michigan - 1 days above AQI 100, with a median AQI of 55.

Explore More

National AQI Rankings → Michigan Full Profile → Michigan Water Quality →

About This Data

Air quality data is from the EPA Air Quality System (AQS), Annual AQI by County dataset. Counties with fewer than 10 monitored days are excluded. "Unhealthy days" counts days with AQI above 100 (Unhealthy for Sensitive Groups or worse). All data is for 2024.

Source: U.S. Environmental Protection Agency, Air Quality System (AQS) U.S. Environmental Protection Agency, Air Quality System (AQS)

Read our methodology - how this data is sourced, computed, and verified.

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Data sourced from the U.S. Environmental Protection Agency (EPA). See our methodology for details. Retrieved and formatted by PlainEnviro Editorial