State air quality · 2025

Montana Air Quality Ranking

Across 23 monitored counties, the typical county in Montana posts a median AQI of 25 (Good) and 85.9% of monitored days were rated Good, from EPA AQS.

25
Avg median AQI
85.9%
Good-air days
23
Counties monitored
92%
Cleaner than US states

Montana's typical county median AQI is 25 (Good) across 23 monitored counties

According to the U.S. EPA Air Quality System, Montana monitors 23 counties with a day-weighted Good-day share of 85.9%. Cleanest: Gallatin County (98.1% Good). Most polluted: Lincoln County (54.4%). These are annual summaries, not live AirNow readings.

Data source EPA Air Quality System (AQS)

Cleaner than US states
Montana's day-weighted Good-day share of 85.9% places it cleaner than 92% of US states.
In-state spread
Within Montana, Gallatin County leads at 98.1% Good days while Lincoln County sits at 54.4% across 23 monitored counties.
2024→2025 release
Montana's Good-day share moved +4.6 points vs the 2024 EPA annual release.
Typical median AQI
Typical median AQI: 25

Verify with AirNow → · EPA AQS →

EPA state monitoring brief

AQS state key MONTANA

Montana · 2025 EPA AQS · 23 counties · med AQI 25 · 85.9% Good · Gallatin→Lincoln spread

  • GOOD 25 Median AQI · Good
  • SHARE 85.9% Good-day share
  • COUNT 23 Counties monitored
  • UNH 10 Unhealthy+ days
  • RANK 92% Cleaner than states
  • PM25 69.8% Main pollutant share

Good-day share peers

Virginia86.5%Montana (this)85.9%Wyoming85.1%Nebraska85%
Good-day share neighbourhood · nearest ABS peers vs Montana

Montana's 85.9% Good-day share is cleaner than 92% of monitored US states; Gallatin and Lincoln County bracket the in-state range. Open Gallatin County →

According to EPA AQS annual summaries on PlainAirData, Montana ranks #4 of 52 by day-weighted good-day share (85.9%) and #3 by mean county median AQI (24.8). Hawaii is #1 of 52 by day-weighted good-day share (93.8% of monitored days) at mean county median-AQI #4 (27.3) ≠ Alaska #1 lowest mean county median AQI (20.3) at good-day share #8 (84.4%).

Data updated August 2026

What changed, what drives it, and how thick is the sample

Three derived views WPR-style word count does not substitute for: release-over-release movement from county annual rows, the EPA main-pollutant day mix, and how many counties sit below the 100-day ranking floor.

Release change

85.9%

Good-day share in 2025, up 4.6 percentage points vs 2024. County-mean median AQI 25, 1.2 points lower (cleaner) than 2024.

Pollutant mix

PM2.5

Main driver on 69.8% of pollutant-assigned days.

  • PM2.5 69.8%
  • Ozone 22.3%
  • PM10 5.6%
  • NO2 1.6%

Monitoring coverage

268

Average monitored days per county in the latest release. 6 of 23 counties sit below the 100-day floor used for cleanest/most-polluted claims.

Counties Monitored

23

Good Days %

85.9%

Avg Median AQI

25

Total Unhealthy Days

10

Best Air Quality

Gallatin County

Worst Air Quality

Lincoln County

Where Montana sits nationally

COUNT-derived placement among 52 US states with at least 365 monitored days in the latest county release. Montana's day-weighted Good-day share is 85.9% - cleaner than 92% of that comparison set.

Montana Good-day share vs. every US state

Day-weighted share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release

85.9% Cleaner than 92% higher than 92% of 52 US states

0.0%–5.0%: 0 US states (0%). Below this entry. 5.0%–10.0%: 0 US states (0%). Below this entry. 10.0%–15.0%: 0 US states (0%). Below this entry. 15.0%–20.0%: 0 US states (0%). Below this entry. 20.0%–25.0%: 0 US states (0%). Below this entry. 25.0%–30.0%: 0 US states (0%). Below this entry. 30.0%–35.0%: 0 US states (0%). Below this entry. 35.0%–40.0%: 0 US states (0%). Below this entry. 40.0%–45.0%: 0 US states (0%). Below this entry. 45.0%–50.0%: 0 US states (0%). Below this entry. 50.0%–55.0%: 0 US states (0%). Below this entry. 55.0%–60.0%: 0 US states (0%). Below this entry. 60.0%–65.0%: 2 US states (4%). Below this entry. 65.0%–70.0%: 9 US states (17%). Below this entry. 70.0%–75.0%: 11 US states (21%). Below this entry. 75.0%–80.0%: 11 US states (21%). Below this entry. 80.0%–85.0%: 13 US states (25%). Below this entry. 85.0%–90.0%: 5 US states (10%). This entry sits in this band. 90.0%–95.0%: 1 US states (2%). Above this entry. 95.0%–100.0%: 0 US states (0%). Above this entry. 100.0%–105.0%: 0 US states (0%). Above this entry. This state 0.0% 100% every floor-qualified US state, bucketed by value

Each bar is a band; taller bars hold more US states. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count, share, and where it sits relative to this entry.

Source U.S. Environmental Protection Agency, Air Quality System (AQS) · 2025

Which counties in Montana have the cleanest and most polluted air?

Cleanest counties in Montana

Share of monitored days rated Good (AQI 0–50)

  1. 1 Gallatin County 98.1%
  2. 2 Rosebud County 98%
  3. 3 Teton County 97.1%
  4. 4 Lake County 96.8%
  5. 5 Beaverhead County 94.7%
  6. 6 Powell County 94.7%
  7. 7 Hill County 92.1%
  8. 8 Glacier County 91.7%
  9. 9 Phillips County 91.4%
  10. 10 Fergus County 90.7%
  11. 11 Dawson County 90.3%
  12. 12 Roosevelt County 87.2%

Good-day share · EPA Air Quality System

County Good % Median AQI
Gallatin 98.1% 11
Rosebud 98.0% 11
Teton 97.1% 12
Lake 96.8% 11
Beaverhead 94.7% 13
Powell 94.7% 13
Hill 92.1% 14
Glacier 91.7% 23
Phillips 91.4% 19
Fergus 90.7% 41
Dawson 90.3% 18
Roosevelt 87.2% 16
Custer 87.2% 40
Sheridan 86.8% 18
Yellowstone 86.3% 38
Silver Bow 84.9% 28
Sanders 82.0% 16
Missoula 81.6% 38
Richland 79.5% 40
Ravalli 79.2% 21
Flathead 73.7% 41
Lewis and Clark 71.5% 44
Cascade 59.8% 46
Lincoln 54.4% 45

Data Sources

Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025. See our methodology for how AQI and median figures are computed.

Coverage: 23 counties in Montana with active monitoring stations. Unmonitored counties are not represented.

Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files, aggregated to the state level · 2020–2025

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.

Informational only, not professional advice. Data from EPA AQS. See our disclaimer.