What is the air quality in Lake County, Montana?

EPA monitors reported only 95 days for Lake County in 2025, below the 100-day floor used for annual conclusions. Within that limited sample, the median AQI was 11 and 92 days were rated Good; this does not describe the full year.

What is the main pollutant in Lake County?

The primary pollutant in Lake County is Fine Particles (PM2.5), which was the main AQI driver on 95 days (100% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.

How many unhealthy air days does Lake County have?

Among 95 reported days in 2025, 0 reached Unhealthy or worse. Because the record is below 100 monitored days, that count cannot establish how many unhealthy days occurred across the full year.

Is the air quality in Lake County getting better or worse?

Air quality in Lake County is stable across floor-qualifying years (2020-2024); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2020 at 94.9% (111 of 117 days). Lowest qualifying Good-day share: 2021 at 89.7% (105 of 117 days).

What does AQI 11 mean for health?

The median of the 95 reported days was AQI 11, in the "Good" category. The limited sample is not enough to assign the county a full-year health grade. See the AQI category guide for day-level meaning and EPA AirNow for current conditions.

How does Lake County compare to other counties in Montana?

Lake County is not placed in county comparisons because its 95-day record is below the 100-day comparison floor.

What is the 90th percentile AQI in Lake County?

The 90th percentile AQI for Lake County is 33, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 79 (Moderate).

Montana · County air quality · 2025

Lake County, Montana

Limited EPA sample: 95 monitored days, below the 100-day floor for a full-year verdict. The figures below describe only those reported days.

Compiled by PlainAirData · August 23, 2026

11
Sample median AQI: 96.8%
Good in sample: 0
Unhealthy in sample: 95
100-day comparison floor

Lake County has only 95 EPA-monitored days in 2025, below the 100-day annual floor

According to the U.S. EPA Air Quality System, Lake County, Montana reported 95 monitored days in 2025. That sample is too thin for a full-year air-quality grade or peer ranking. Use the figures only as the reported-day record, and check AirNow for current conditions.

Data source EPA Air Quality System (AQS)

Monitored days: Lake County reported 95 monitored days in 2025, below the 100-day floor: sample-only, not a full-year peer rank.
Sample median AQI: Sample median AQI: 11
Annual floor: Annual floor: 100

Lake County's peak single-day AQI fell from 157 to 77 between the 2023 and 2024 EPA annual releases, a change of -80 points.
Lake County's median AQI fell from 13 to 9 between the 2023 and 2024 EPA annual releases, a change of -4 points.
Lake County's Good-day share rose from 92.7% to 93.9% between the 2023 and 2024 EPA annual releases, a change of +1.3 percentage points.
Lake County's Unhealthy-category days fell from 1 to 0 between the 2023 and 2024 EPA annual releases, a change of -1 days.

Data updated August 2026

Good · 92 d · 96.8%
Moderate · 3 d · 3.2%

How did Lake County's reported sample break down in 2025?

Across 95 monitored days, 92 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 79 (Moderate).

EPA AQS →

Pollutant Breakdown

Days where each pollutant was the primary driver of AQI readings in Lake County.

PM2.5 · 95 days · 100.0%

Sample Coverage and Health Context

Limited sample

Lake County has no annual health grade because only 95 days were reported, below the 100-day floor. The 96.8% Good-day share describes only that sample.

Reported days do not reveal what happened during unmonitored parts of the year, including seasonal smoke, ozone, or inversion periods. Use these values as a description of the available EPA sample only, and check AirNow.gov for current health guidance.

The dominant pollutant is PM2.5, driving AQI on 95 of 95 monitored days.

5-Year Air Quality Trend

Air quality is stable in Lake County. Highest Good-day share: 2020 (94.9%, 111 of 117 monitored days). The 2025 row is shown for transparency but excluded from the direction because it has fewer than 100 monitored days.

Year	Good	Moderate	USG	Unhealthy	Median AQI	Max AQI
2020	111	3	1	2	7	183
2021	105	9	2	1	9	152
2022	93	3	1	0	11	120
2023	101	6	1	1	13	157
2024	108	7	0	0	9	77
2025	92	3	0	0	11	79

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 Lake County, Montana · 2020–2025 Accessed 2026-08-23

Download this county's annual AQI row as CSV , with the same EPA fields and denominator shown on this page.

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.