Median AQI
43
Good
Michigan · County air quality · 2025
Allegan County, Michigan
Median AQI 43 (Good). 71.2% of monitored days rated Good, direct from EPA Air Quality System stations.
- 43
- Median AQI
- 71.2%
- Good-air days
- 1
- Unhealthy days
- 33%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Allegan County's air is good on balance, more polluted than the median US county, a median AQI of 43 with 71.2% of 302 monitored days in the Good band, driven mainly by Ozone.
- 43
- median AQI · Good
- 71.2%
- days rated Good
- Ozone
- main pollutant
- 33%
- cleaner than US counties
1 day reached Unhealthy or worse; the worst single reading hit AQI 151.
Data updated July 2026
- Good · 215 d · 71.2%
- Moderate · 76 d · 25.2%
- USG · 10 d · 3.3%
- Unhealthy · 1 d · 0.3%
How did Allegan County's air break down in 2025?
Across 302 monitored days, 215 fell in the Good band (AQI 0–50) and 1 reached Unhealthy or worse. The worst single day peaked at AQI 151 (Unhealthy).
EPA AQS →Air quality data from EPA Air Quality System (2025). 302 days monitored. Median AQI: 43 (Good).
Insights: Allegan County, Michigan. EPA monitors recorded a median Air Quality Index of 43 across 302 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 215 (71%) fell in the Good band (AQI 0–50), 76 (25%) registered Moderate readings, and 10 (3%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 74, while the worst single-day peak hit 151 (Unhealthy). Residents averaged about 21.4 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (214 days), PM2.5 (88 days). Across the 2020–2025 trend window, good days shifted by -60 and the median AQI moved +6 points, placing the multi-year trajectory at worsening. Residents and visitors experienced 1 unhealthy-or-worse days combined, periods when the EPA recommends sensitive groups limit prolonged outdoor exertion. Nearby counties show comparable readings: Bay (71.8% good, AQI 38); Benzie (91.1% good, AQI 35); Berrien (80.9% good, AQI 41); Cass (85.3% good, AQI 40); Clinton (90.2% good, AQI 39); Genesee (83.2% good, AQI 38).
Air Quality Summary
Good Days
71.2%
215 of 302 monitored days
-3.8pp vs 75% target
Max AQI Recorded
151
Unhealthy
Health Grade
Moderate
90th-pct AQI 74
Allegan County, Good days share 71.2%
National avg
Share of monitored days at AQI 0-50 (Good band).
Allegan County, Unhealthy-or-worse share 0.3%
National avg
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
AQI Day Breakdown (2025)
Distribution of 302 monitored days across EPA AQI categories.
Good
215
71%
Moderate
76
25%
USG
10
3%
Unhealthy
1
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Allegan County.
- Ozone · 214 days · 70.9%
- PM2.5 · 88 days · 29.1%
Health Impact Assessment
Moderate
Allegan County's air quality is rated Moderate based on 71.2% good air days. There were 1 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 10 days reached "Unhealthy for Sensitive Groups" (AQI 101-150) and peak AQI reached 151. Sensitive groups should monitor real-time conditions at AirNow.gov.
The dominant pollutant is Ozone, driving AQI on 214 of 302 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Allegan County. Best year: 2020 (275 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 275 | 78 | 6 | 0 | 37 | 136 |
| 2021 | 245 | 107 | 9 | 0 | 42 | 136 |
| 2022 | 256 | 82 | 4 | 2 | 40 | 195 |
| 2023 | 246 | 102 | 11 | 1 | 42 | 161 |
| 2024 | 222 | 125 | 4 | 0 | 46 | 115 |
| 2025 | 215 | 76 | 10 | 1 | 43 | 151 |
How does Allegan County compare?
How Allegan County compares
Good-day share worse than US avg
Allegan County 71.2%
Bay County, Michigan 71.8%
US average 76.5%
Median AQI worse than US avg
Allegan County 43
Bay County, Michigan 38
US average 38
Unhealthy days / yr worse than US avg
Allegan County 1
Bay County, Michigan 0
US average 0
Other Counties in Michigan
Air quality comparison for nearby counties in Michigan.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Allegan County.
Allen County, Ohio
AQI 43 · 65.9% good
Ashtabula County, Ohio
AQI 43 · 81.2% good
Bell County, Kentucky
AQI 43 · 63.5% good
Boise County, Idaho
AQI 43 · 72.9% good
Brazos County, Texas
AQI 43 · 63.4% good
Broward County, Florida
AQI 43 · 72.4% good
What Allegan County's air means for you
On most days the air here is fine, but Ozone drives 1 unhealthy-or-worse day a year that sensitive groups should plan around.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 43 means for exposure. Health guidance
- See how Allegan County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Allegan County with its Michigan neighbours before drawing a conclusion about the region. All of Michigan
Based on 302 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
More Air Quality Data
Air Quality Guides
Frequently Asked Questions
What is the air quality in Allegan County, Michigan? ▼
Allegan County has a median Air Quality Index (AQI) of 43, rated "Good." 71.2% of monitored days (215 out of 302) had good air quality in 2025.
What is the main pollutant in Allegan County? ▼
The primary pollutant in Allegan County is Ozone (O3), which was the main AQI driver on 214 days (71% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Allegan County have? ▼
In 2025, Allegan County recorded 1 unhealthy air days (1 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 151.
Is the air quality in Allegan County getting better or worse? ▼
Air quality in Allegan County is worsening based on 5-year trends (2020-2025). Best year: 2020 with 275 good days. Worst year: 2025 with 215 good days.
What does AQI 43 mean for health? ▼
Allegan County's median AQI of 43 falls in the "Good" category. See the <a href="/guides/understanding-aqi" class="underline">AQI category guide</a> for what each range means for health.
How does Allegan County compare to other counties in Michigan? ▼
Allegan County has 71.2% good air days. Nearby counties in Michigan: Bay (71.8% good), Benzie (91.1% good), Berrien (80.9% good), Cass (85.3% good), Clinton (90.2% good), Genesee (83.2% good).
What is the 90th percentile AQI in Allegan County? ▼
The 90th percentile AQI for Allegan County is 74, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 151 (Unhealthy).
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025 (aqs.epa.gov). For current conditions (not shown here — this page is historical annual data), see EPA AirNow (airnow.gov). See our methodology for how AQI, median, and coverage figures are computed.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer.
Every figure on PlainAir is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.