Median AQI
13
Good
Montana · County air quality · 2025
Hill County, Montana
Median AQI 13 (Good). 94.6% of monitored days rated Good, direct from EPA Air Quality System stations.
- 13
- Median AQI
- 94.6%
- Good-air days
- 1
- Unhealthy days
- 88%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Hill County's air is good on balance, cleaner than most US counties, a median AQI of 13 with 94.6% of 149 monitored days in the Good band, driven mainly by PM2.5.
- 13
- median AQI · Good
- 94.6%
- days rated Good
- PM2.5
- main pollutant
- 88%
- cleaner than US counties
1 day reached Unhealthy or worse; the worst single reading hit AQI 157.
Data updated July 2026
- Good · 141 d · 94.6%
- Moderate · 7 d · 4.7%
- Unhealthy · 1 d · 0.7%
How did Hill County's air break down in 2025?
Across 149 monitored days, 141 fell in the Good band (AQI 0–50) and 1 reached Unhealthy or worse. The worst single day peaked at AQI 157 (Unhealthy).
EPA AQS →Air quality data from EPA Air Quality System (2025). 149 days monitored. Median AQI: 13 (Good).
Insights: Hill County, Montana. EPA monitors recorded a median Air Quality Index of 13 across 149 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 141 (95%) fell in the Good band (AQI 0–50), 7 (5%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 34, while the worst single-day peak hit 157 (Unhealthy). Residents averaged about 28.4 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (149 days). Across the 2023–2025 trend window, good days shifted by -29 and the median AQI moved -10 points, placing the multi-year trajectory at improving. 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: 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
94.6%
141 of 149 monitored days
19.6pp vs 75% target
Max AQI Recorded
157
Unhealthy
Health Grade
Excellent
90th-pct AQI 34
Hill County, Good days share 94.6%
National avg
Share of monitored days at AQI 0-50 (Good band).
Hill County, Unhealthy-or-worse share 0.7%
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 149 monitored days across EPA AQI categories.
Good
141
95%
Moderate
7
5%
USG
0
0%
Unhealthy
1
1%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Hill County.
- PM2.5 · 149 days · 100.0%
Health Impact Assessment
Excellent
Hill County's air quality is rated Excellent based on 94.6% good air days. There were 1 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 0 days reached "Unhealthy for Sensitive Groups" (AQI 101-150) and peak AQI reached 157. Sensitive groups should monitor real-time conditions at AirNow.gov.
The dominant pollutant is PM2.5, driving AQI on 149 of 149 monitored days.
5-Year Air Quality Trend
Air quality is improving in Hill County. Best year: 2024 (314 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2023 | 170 | 38 | 2 | 3 | 23 | 215 |
| 2024 | 314 | 23 | 2 | 0 | 15 | 123 |
| 2025 | 141 | 7 | 0 | 1 | 13 | 157 |
How does Hill County compare?
How Hill County compares
Good-day share better than US avg
Hill County 94.6%
Beaverhead County, Montana 100.0%
US average 76.5%
Median AQI better than US avg
Hill County 13
Beaverhead County, Montana 12
US average 38
Unhealthy days / yr worse than US avg
Hill County 1
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 Hill County.
Sheridan County, Montana
AQI 13 · 100.0% 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 Hill County's air means for you
On most days the air here is fine, but PM2.5 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-PM2.5 days, the guide explains what a median of 13 means for exposure. Health guidance
- See how Hill County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Hill County with its Montana neighbours before drawing a conclusion about the region. All of Montana
Based on 149 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 Hill County, Montana? ▼
Hill County has a median Air Quality Index (AQI) of 13, rated "Good." 94.6% of monitored days (141 out of 149) had good air quality in 2025.
What is the main pollutant in Hill County? ▼
The primary pollutant in Hill County is Fine Particles (PM2.5), which was the main AQI driver on 149 days (100% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Hill County have? ▼
In 2025, Hill County recorded 1 unhealthy air days (1 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 157.
Is the air quality in Hill County getting better or worse? ▼
Air quality in Hill County is improving based on 5-year trends (2023-2025). Best year: 2024 with 314 good days. Worst year: 2025 with 141 good days.
What does AQI 13 mean for health? ▼
Hill 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 Hill County compare to other counties in Montana? ▼
Hill County has 94.6% 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 Hill County? ▼
The 90th percentile AQI for Hill County is 34, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 157 (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.