Median AQI
13
Good
Montana · County air quality · 2025
Sheridan County, Montana
Median AQI 13 (Good). 100.0% of monitored days rated Good, direct from EPA Air Quality System stations.
- 13
- Median AQI
- 100.0%
- Good-air days
- 0
- Unhealthy days
- 96%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Sheridan County's air is good on balance, among the cleanest 5% of US counties, a median AQI of 13 with 100.0% of 19 monitored days in the Good band, driven mainly by PM2.5.
- 13
- median AQI · Good
- 100.0%
- days rated Good
- PM2.5
- main pollutant
- 96%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 31.
Data updated July 2026
- Good · 19 d · 100.0%
How did Sheridan County's air break down in 2025?
Across 19 monitored days, 19 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 31 (Good).
EPA AQS →Air quality data from EPA Air Quality System (2025). 19 days monitored. Median AQI: 13 (Good).
Insights: Sheridan County, Montana. EPA monitors recorded a median Air Quality Index of 13 across 19 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 19 (100%) fell in the Good band (AQI 0–50), 0 (0%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 30, while the worst single-day peak hit 31 (Good). Residents averaged about 30.0 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (19 days). Across the 2020–2025 trend window, good days shifted by -84 and the median AQI moved +0 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 31, good 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); Fergus (92.2% good, AQI 44); Flathead (82.1% good, AQI 40); Gallatin (99.1% good, AQI 14).
Air Quality Summary
Good Days
100.0%
19 of 19 monitored days
25.0pp vs 75% target
Max AQI Recorded
31
Good
Health Grade
Excellent
90th-pct AQI 30
Sheridan County, Good days share 100.0%
National avg
Share of monitored days at AQI 0-50 (Good band).
Sheridan 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 19 monitored days across EPA AQI categories.
Good
19
100%
Moderate
0
0%
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 Sheridan County.
- PM2.5 · 19 days · 100.0%
Health Impact Assessment
Excellent
Sheridan County's air quality is rated Excellent based on 100.0% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 100.0% of monitored days in 2025, with a median AQI of 13. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 19 of 19 monitored days.
5-Year Air Quality Trend
Air quality is improving in Sheridan County. Best year: 2021 (108 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 103 | 4 | 0 | 0 | 13 | 58 |
| 2021 | 108 | 12 | 0 | 0 | 17 | 98 |
| 2022 | 85 | 4 | 0 | 0 | 16 | 66 |
| 2023 | 96 | 12 | 3 | 1 | 18 | 160 |
| 2024 | 104 | 13 | 2 | 0 | 17 | 126 |
| 2025 | 19 | 0 | 0 | 0 | 13 | 31 |
How does Sheridan County compare?
How Sheridan County compares
Good-day share better than US avg
Sheridan County 100.0%
Beaverhead County, Montana 100.0%
US average 76.5%
Median AQI better than US avg
Sheridan County 13
Beaverhead County, Montana 12
US average 38
Unhealthy days / yr about average
Sheridan 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 Sheridan County.
Hill County, Montana
AQI 13 · 94.6% good
Apache County, Arizona
AQI 14 · 99.6% good
Beaverhead County, Montana
AQI 12 · 100.0% good
Columbiana County, Ohio
AQI 12 · 100.0% good
Cook County, Minnesota
AQI 12 · 100.0% good
Dawson County, Montana
AQI 14 · 95.0% good
What Sheridan County's air means for you
The air here stays in the breathable range year-round, with PM2.5 the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-PM2.5 days, the guide explains what a median of 13 means for exposure. Health guidance
- See how Sheridan County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Sheridan County with its Montana neighbours before drawing a conclusion about the region. All of Montana
Based on 19 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 Sheridan County, Montana? ▼
Sheridan County has a median Air Quality Index (AQI) of 13, rated "Good." 100.0% of monitored days (19 out of 19) had good air quality in 2025.
What is the main pollutant in Sheridan County? ▼
The primary pollutant in Sheridan County is Fine Particles (PM2.5), which was the main AQI driver on 19 days (100% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Sheridan County have? ▼
In 2025, Sheridan County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 31.
Is the air quality in Sheridan County getting better or worse? ▼
Air quality in Sheridan County is improving based on 5-year trends (2020-2025). Best year: 2021 with 108 good days. Worst year: 2025 with 19 good days.
What does AQI 13 mean for health? ▼
Sheridan County's median AQI of 13 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 Sheridan County compare to other counties in Montana? ▼
Sheridan County has 100.0% good air days. Nearby counties in Montana: Beaverhead (100.0% good), Custer (91.2% good), Dawson (95.0% good), Fergus (92.2% good), Flathead (82.1% good), Gallatin (99.1% good).
What is the 90th percentile AQI in Sheridan County? ▼
The 90th percentile AQI for Sheridan County is 30, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 31 (Good).
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.