Median AQI
45
Good
Montana · County air quality · 2025
Lincoln County, Montana
Median AQI 45 (Good). 54.4% of monitored days rated Good, direct from EPA Air Quality System stations.
- 45
- Median AQI
- 54.4%
- Good-air days
- 0
- Unhealthy days
- 9%
- Cleaner than US counties
Lincoln County's 2025 annual median AQI is 45 (Good), with 54.4% Good days
According to the U.S. EPA Air Quality System, Lincoln County, Montana posted a 2025 median AQI of 45 (Good) across 182 monitored days, with 54.4% rated Good and 0 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Lincoln County's 54.4% Good-day share places it cleaner than 9% of US counties in 2025.
- Closest median-AQI peer
- Baltimore County (64.7% Good, median AQI 45) is the closest nationwide median-AQI peer to Lincoln County.
- 2020–2025 trend
- Lincoln County's floor-qualifying Good-day share is improving from 2020 to 2025 (48.2% → 54.4%).
- Median AQI
- Median AQI: 45
The verdict
According to EPA Air Quality System monitoring data, Lincoln County's air is good on balance, among the most polluted counties nationally, a median AQI of 45 with 54.4% of 182 monitored days in the Good band, driven mainly by PM2.5.
- 45
- median AQI · Good
- 54.4%
- days rated Good
- PM2.5
- main pollutant
- 9%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 118.
Annual release change
What changed in the 2025 EPA annual release
- Lincoln County's Good-day share rose from 50.7% to 54.4% between the 2024 and 2025 EPA annual releases, a change of +3.7 percentage points.
- Lincoln County's median AQI fell from 49 to 45 between the 2024 and 2025 EPA annual releases, a change of -4 points.
Data updated August 2026
- Good · 99 d · 54.4%
- Moderate · 81 d · 44.5%
- USG · 2 d · 1.1%
How did Lincoln County's air break down in 2025?
Across 182 monitored days, 99 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 118 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 182 days monitored. Median AQI: 45 (Good).
Insights: Lincoln County, Montana. EPA monitors recorded a median Air Quality Index of 45 across 182 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 99 (54%) fell in the Good band (AQI 0–50), 81 (45%) registered Moderate readings, and 2 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 67, while the worst single-day peak hit 118 (USG). Residents averaged about 16.3 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (181 days), PM10 (1 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by +6.6 points (measured against 366 monitored days in 2020 and 182 in 2025, so raw day counts are not comparable) and the median AQI moved -7 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 118, usg but never Unhealthy. 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
54.4%
99 of 182 monitored days
-20.6pp vs 75% target
Max AQI Recorded
118
USG
Health Grade
Moderate
90th-pct AQI 67
Lincoln County, Good days share 54.4%
National avg
Share of monitored days at AQI 0-50 (Good band).
Lincoln 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 182 monitored days across EPA AQI categories.
Good
99
54%
Moderate
81
45%
USG
2
1%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Lincoln County.
- PM2.5 · 181 days · 99.5%
- PM10 · 1 days · 0.5%
Health Impact Assessment
Moderate
Lincoln County's air quality is rated Moderate based on 54.4% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 54.4% of monitored days in 2025, with a median AQI of 45. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 181 of 182 monitored days.
5-Year Air Quality Trend
Air quality is improving in Lincoln County. Highest Good-day share: 2025 (54.4%, 99 of 182 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 175 | 182 | 2 | 4 | 52 | 403 |
| 2021 | 125 | 223 | 11 | 6 | 56 | 177 |
| 2022 | 184 | 175 | 4 | 2 | 49 | 174 |
| 2023 | 151 | 209 | 2 | 2 | 53 | 189 |
| 2024 | 185 | 178 | 2 | 0 | 49 | 116 |
| 2025 | 99 | 81 | 2 | 0 | 45 | 118 |
How does Lincoln County compare?
How Lincoln County compares
Good-day share worse than typical
Lincoln County 54.4%
Baltimore County, Maryland 64.7%
Typical US county 76.0%
Median AQI worse than typical
Lincoln County 45
Baltimore County, Maryland 45
Typical US county 39
Unhealthy days / yr better than typical
Lincoln County 0
Baltimore County, Maryland 0
Typical US county 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Lincoln County (45), not geographic neighbors.
Baltimore County, Maryland
Median AQI 45 · 64.7% Good-day share
Bell County, Texas
Median AQI 45 · 66.0% Good-day share
Box Elder County, Utah
Median AQI 45 · 64.7% Good-day share
Bronx County, New York
Median AQI 45 · 59.2% Good-day share
Catano County, Puerto Rico
Median AQI 45 · 60.6% Good-day share
Catron County, New Mexico
Median AQI 45 · 71.7% 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).
Muscogee County, Georgia
54.5% Good-day share · median AQI 48
Fulton County, Georgia
54.3% Good-day share · median AQI 49
Clayton County, Georgia
54.1% Good-day share · median AQI 48
Bowie County, Texas
55.0% Good-day share · median AQI 48
Spartanburg County, South Carolina
55.1% Good-day share · median AQI 48
Ottawa County, Oklahoma
53.7% Good-day share · median AQI 49
Montana counties on the map
Geographic containment only, other monitored counties in Montana, independent of AQI or pollutant match.
What Lincoln 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 45 means for exposure. Health guidance
- See how Lincoln County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Lincoln County with its Montana neighbours before drawing a conclusion about the region. All of Montana
Based on 182 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 Lincoln County, Montana? ▼
Lincoln County has a median Air Quality Index (AQI) of 45, rated "Good." 54.4% of monitored days (99 out of 182) had good air quality in 2025.
What is the main pollutant in Lincoln County? ▼
The primary pollutant in Lincoln County is Fine Particles (PM2.5), which was the main AQI driver on 181 days (99% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Lincoln County have? ▼
In 2025, Lincoln County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 118.
Is the air quality in Lincoln County getting better or worse? ▼
Air quality in Lincoln County is improving across floor-qualifying years (2020-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2025 at 54.4% (99 of 182 days). Lowest qualifying Good-day share: 2021 at 34.2% (125 of 365 days).
What does AQI 45 mean for health? ▼
Lincoln County's median AQI of 45 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Lincoln County compare to other counties in Montana? ▼
Lincoln County has 54.4% 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 Lincoln County? ▼
The 90th percentile AQI for Lincoln County is 67, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 118 (USG).
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 Lincoln 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.