Median AQI
14
Good
Montana · County air quality · 2025
Hill County, Montana
Median AQI 14 (Good). 92.1% of monitored days rated Good, direct from EPA Air Quality System stations.
- 14
- Median AQI
- 92.1%
- Good-air days
- 1
- Unhealthy days
- 85%
- Cleaner than US counties
Hill County's 2025 annual median AQI is 14 (Good), with 92.1% Good days
According to the U.S. EPA Air Quality System, Hill County, Montana posted a 2025 median AQI of 14 (Good) across 304 monitored days, with 92.1% rated Good and 1 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Hill County's 92.1% Good-day share places it cleaner than 85% of US counties in 2025.
- Closest median-AQI peer
- Beaverhead County (94.7% Good, median AQI 13) is the closest nationwide median-AQI peer to Hill County.
- 2023–2025 trend
- Hill County's floor-qualifying Good-day share is improving from 2023 to 2025 (79.8% → 92.1%).
- Median AQI
- Median AQI: 14
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 14 with 92.1% of 304 monitored days in the Good band, driven mainly by PM2.5.
- 14
- median AQI · Good
- 92.1%
- days rated Good
- PM2.5
- main pollutant
- 85%
- cleaner than US counties
1 day reached Unhealthy or worse; the worst single reading hit AQI 157.
Annual release change
What changed in the 2025 EPA annual release
- Hill County's peak single-day AQI rose from 123 to 157 between the 2024 and 2025 EPA annual releases, a change of +34 points.
- Hill County's Unhealthy-category days rose from 0 to 1 between the 2024 and 2025 EPA annual releases, a change of +1 days.
Data updated August 2026
- Good · 280 d · 92.1%
- Moderate · 22 d · 7.2%
- USG · 1 d · 0.3%
- Unhealthy · 1 d · 0.3%
How did Hill County's air break down in 2025?
Across 304 monitored days, 280 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). 304 days monitored. Median AQI: 14 (Good).
Insights: Hill County, Montana. EPA monitors recorded a median Air Quality Index of 14 across 304 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 280 (92%) fell in the Good band (AQI 0–50), 22 (7%) registered Moderate readings, and 1 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 40, while the worst single-day peak hit 157 (Unhealthy). Residents averaged about 27.6 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (304 days). Across the 2023–2025 trend window, the share of monitored days rated Good shifted by +12.7 points (measured against 214 monitored days in 2023 and 304 in 2025, so raw day counts are not comparable) and the median AQI moved -9 points, placing the multi-year trajectory at improving. The annual record contains 1 day at Unhealthy or worse. On that day, the EPA recommends that sensitive groups limit prolonged outdoor exertion. Nearby counties show comparable readings: Beaverhead (94.7% good, AQI 13); Cascade (59.8% good, AQI 46); Custer (87.2% good, AQI 40); Dawson (90.3% good, AQI 18); Fergus (90.7% good, AQI 41); Flathead (73.7% good, AQI 41).
Air Quality Summary
Good Days
92.1%
280 of 304 monitored days
17.1pp vs 75% target
Max AQI Recorded
157
Unhealthy
Health Grade
Excellent
90th-pct AQI 40
Hill County, Good days share 92.1%
National avg
Share of monitored days at AQI 0-50 (Good band).
Hill County, Unhealthy-or-worse share 3.3%
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 304 monitored days across EPA AQI categories.
Good
280
92%
Moderate
22
7%
USG
1
0%
Unhealthy
1
0%
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 · 304 days · 100.0%
Health Impact Assessment
Excellent
Hill County's air quality is rated Excellent based on 92.1% good air days. There were 1 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 1 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 304 of 304 monitored days.
5-Year Air Quality Trend
Air quality is improving in Hill County. Highest Good-day share: 2024 (92.6%, 314 of 339 monitored 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 | 280 | 22 | 1 | 1 | 14 | 157 |
How does Hill County compare?
How Hill County compares
Good-day share better than typical
Hill County 92.1%
Beaverhead County, Montana 94.7%
Typical US county 76.0%
Median AQI better than typical
Hill County 14
Beaverhead County, Montana 13
Typical US county 39
Unhealthy days / yr about typical
Hill County 1
Beaverhead County, Montana 0
Typical US county 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Hill County (14), not geographic neighbors.
Beaverhead County, Montana
Median AQI 13 · 94.7% Good-day share
Navajo County, Arizona
Median AQI 13 · 99.5% Good-day share
Park County, Wyoming
Median AQI 13 · 98.0% Good-day share
Platte County, Wyoming
Median AQI 15 · 90.6% Good-day share
Windham County, Vermont
Median AQI 15 · 92.0% Good-day share
Cook County, Minnesota
Median AQI 16 · 88.0% Good-day share
Same primary pollutant: PM2.5
PM2.5 led the AQI on the most monitored days here. These peers share that driver and the closest Good-day share (a second relationship type beyond median-AQI neighbors).
Pitkin County, Colorado
92.3% Good-day share · median AQI 19
Glacier County, Montana
91.7% Good-day share · median AQI 23
Garfield County, Washington
92.5% Good-day share · median AQI 19
Prowers County, Colorado
92.6% Good-day share · median AQI 27
Alamosa County, Colorado
91.5% Good-day share · median AQI 25
Matanuska-Susitna County, Alaska
91.5% Good-day share · median AQI 9
Montana counties on the map
Geographic containment only, other monitored counties in Montana, independent of AQI or pollutant match.
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 14 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 304 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
Keep exploring the annual AQI record
Air-quality reading list
Frequently Asked Questions
What is the air quality in Hill County, Montana? ▼
Hill County has a median Air Quality Index (AQI) of 14, rated "Good." 92.1% of monitored days (280 out of 304) 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 304 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 across floor-qualifying years (2023-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2024 at 92.6% (314 of 339 days). Lowest qualifying Good-day share: 2023 at 79.8% (170 of 214 days).
What does AQI 14 mean for health? ▼
Hill County's median AQI of 14 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Hill County compare to other counties in Montana? ▼
Hill County has 92.1% good air days. Nearby counties in Montana: Beaverhead (94.7% good), Cascade (59.8% good), Custer (87.2% good), Dawson (90.3% good), Fergus (90.7% good), Flathead (73.7% good).
What is the 90th percentile AQI in Hill County? ▼
The 90th percentile AQI for Hill County is 40, 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. Spotted a figure that looks wrong? Report a correction.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files for Hill County, Montana · 2020–2025
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Every figure on PlainAirData 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.