Median AQI
44
Good
Montana · County air quality · 2025
Fergus County, Montana
Median AQI 44 (Good). 92.2% of monitored days rated Good, direct from EPA Air Quality System stations.
- 44
- Median AQI
- 92.2%
- Good-air days
- 0
- Unhealthy days
- 81%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Fergus County's air is good on balance, cleaner than most US counties, a median AQI of 44 with 92.2% of 180 monitored days in the Good band, driven mainly by Ozone.
- 44
- median AQI · Good
- 92.2%
- days rated Good
- Ozone
- main pollutant
- 81%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 87.
Data updated July 2026
- Good · 166 d · 92.2%
- Moderate · 14 d · 7.8%
How did Fergus County's air break down in 2025?
Across 180 monitored days, 166 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 87 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 180 days monitored. Median AQI: 44 (Good).
Insights: Fergus County, Montana. EPA monitors recorded a median Air Quality Index of 44 across 180 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 166 (92%) fell in the Good band (AQI 0–50), 14 (8%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 49, while the worst single-day peak hit 87 (Moderate). Residents averaged about 27.7 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (168 days), PM2.5 (12 days). Across the 2020–2025 trend window, good days shifted by -164 and the median AQI moved +5 points, placing the multi-year trajectory at stable. The worst single reading over the 2020–2025 window was AQI 87, moderate but never Unhealthy. Nearby counties show comparable readings: Beaverhead (100.0% good, AQI 12); Custer (91.2% good, AQI 39); Dawson (95.0% good, AQI 14); Flathead (82.1% good, AQI 40); Gallatin (99.1% good, AQI 14); Glacier (96.4% good, AQI 22).
Air Quality Summary
Good Days
92.2%
166 of 180 monitored days
17.2pp vs 75% target
Max AQI Recorded
87
Moderate
Health Grade
Excellent
90th-pct AQI 49
Fergus County, Good days share 92.2%
National avg
Share of monitored days at AQI 0-50 (Good band).
Fergus County, Unhealthy-or-worse share 0.0%
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 180 monitored days across EPA AQI categories.
Good
166
92%
Moderate
14
8%
USG
0
0%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Fergus County.
- Ozone · 168 days · 93.3%
- PM2.5 · 12 days · 6.7%
Health Impact Assessment
Excellent
Fergus County's air quality is rated Excellent based on 92.2% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 92.2% of monitored days in 2025, with a median AQI of 44. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 168 of 180 monitored days.
5-Year Air Quality Trend
Air quality is stable in Fergus County. Best year: 2022 (341 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 330 | 33 | 1 | 2 | 39 | 159 |
| 2021 | 288 | 62 | 14 | 1 | 41 | 156 |
| 2022 | 341 | 22 | 2 | 0 | 40 | 122 |
| 2023 | 315 | 43 | 4 | 2 | 41 | 185 |
| 2024 | 312 | 50 | 3 | 1 | 40 | 155 |
| 2025 | 166 | 14 | 0 | 0 | 44 | 87 |
How does Fergus County compare?
How Fergus County compares
Good-day share better than US avg
Fergus County 92.2%
Beaverhead County, Montana 100.0%
US average 76.5%
Median AQI worse than US avg
Fergus County 44
Beaverhead County, Montana 12
US average 38
Unhealthy days / yr about average
Fergus County 0
Beaverhead County, Montana 0
US average 0
Other Counties in Montana
Air quality comparison for nearby counties in Montana.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Fergus County.
Baltimore County, Maryland
AQI 44 · 70.4% good
Baltimore (City) County, Maryland
AQI 44 · 68.7% good
Bartholomew County, Indiana
AQI 44 · 69.2% good
Berks County, Pennsylvania
AQI 44 · 65.6% good
Bolivar County, Mississippi
AQI 44 · 70.3% good
Brewster County, Texas
AQI 44 · 69.0% good
What Fergus County's air means for you
The air here stays in the breathable range year-round, with Ozone the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 44 means for exposure. Health guidance
- See how Fergus County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Fergus County with its Montana neighbours before drawing a conclusion about the region. All of Montana
Based on 180 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 Fergus County, Montana? ▼
Fergus County has a median Air Quality Index (AQI) of 44, rated "Good." 92.2% of monitored days (166 out of 180) had good air quality in 2025.
What is the main pollutant in Fergus County? ▼
The primary pollutant in Fergus County is Ozone (O3), which was the main AQI driver on 168 days (93% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Fergus County have? ▼
In 2025, Fergus County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 87.
Is the air quality in Fergus County getting better or worse? ▼
Air quality in Fergus County is stable based on 5-year trends (2020-2025). Best year: 2022 with 341 good days. Worst year: 2025 with 166 good days.
What does AQI 44 mean for health? ▼
Fergus County's median AQI of 44 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 Fergus County compare to other counties in Montana? ▼
Fergus County has 92.2% good air days. Nearby counties in Montana: Beaverhead (100.0% good), Custer (91.2% good), Dawson (95.0% good), Flathead (82.1% good), Gallatin (99.1% good), Glacier (96.4% good).
What is the 90th percentile AQI in Fergus County? ▼
The 90th percentile AQI for Fergus County is 49, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 87 (Moderate).
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.