Data / Rankings / Share of days with good air quality (US EPA AQI) / Counties in Montana

Counties in Montana by share of days with good air quality (US EPA AQI), 2025

Gallatin County had the highest share of days with good air quality (US EPA AQI) of 23 counties in 2025, at 98.1%. Lincoln County had the lowest, at 54.4%. The median was 87.2%. Source: EPA.

Keep it in a collection in your library.
Highest98.1Gallatin County
Lowest54.4Lincoln County
Median87.223 counties

Map of counties, 2025

Beaverhead County: 94.7 %Custer County: 87.2 %Dawson County: 90.3 %Fergus County: 90.7 %Flathead County: 73.7 %Gallatin County: 98.1 %Glacier County: 91.7 %Hill County: 92.1 %Lake County: 96.8 %Lewis and Clark County: 71.5 %Lincoln County: 54.4 %Missoula County: 81.6 %Phillips County: 91.4 %Powell County: 94.7 %Ravalli County: 79.2 %Richland County: 79.5 %Roosevelt County: 87.2 %Rosebud County: 98 %Sanders County: 82 %Sheridan County: 86.8 %Silver Bow County: 84.9 %Teton County: 97.1 %Yellowstone County: 86.3 %
  • Under 80
  • 80 to 87
  • 87 to 91
  • 91 to 95
  • 95 and over
  • No data
%, 2025. Hatched areas have no value for this period. Source: Invokely calculation with data from EPA. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2025

Gallatin County: 98.1 %Gallatin County98.1Rosebud County: 98 %Rosebud County98Teton County: 97.1 %Teton County97.1Lake County: 96.8 %Lake County96.8Beaverhead County: 94.7 %Beaverhead County94.7Powell County: 94.7 %Powell County94.7Hill County: 92.1 %Hill County92.1Glacier County: 91.7 %Glacier County91.7Phillips County: 91.4 %Phillips County91.4Fergus County: 90.7 %Fergus County90.7Dawson County: 90.3 %Dawson County90.3Custer County: 87.2 %Custer County87.2Roosevelt County: 87.2 %Roosevelt County87.2Sheridan County: 86.8 %Sheridan County86.8Yellowstone County: 86.3 %Yellowstone County86.3Silver Bow County: 84.9 %Silver Bow County84.9Sanders County: 82 %Sanders County82Missoula County: 81.6 %Missoula County81.6Richland County: 79.5 %Richland County79.5Ravalli County: 79.2 %Ravalli County79.2Flathead County: 73.7 %Flathead County73.7Lewis and Clark County: 71.5 %Lewis and Clark County71.5Lincoln County: 54.4 %Lincoln County54.4Gallatin County: 98.1 %Gallatin County98.1Rosebud County: 98 %Rosebud County98Teton County: 97.1 %Teton County97.1Lake County: 96.8 %Lake County96.8Beaverhead County: 94.7 %Beaverhead County94.7Powell County: 94.7 %Powell County94.7Hill County: 92.1 %Hill County92.1Glacier County: 91.7 %Glacier County91.7Phillips County: 91.4 %Phillips County91.4Fergus County: 90.7 %Fergus County90.7Dawson County: 90.3 %Dawson County90.3Custer County: 87.2 %Custer County87.2Roosevelt County: 87.2 %Roosevelt County87.2Sheridan County: 86.8 %Sheridan County86.8Yellowstone County: 86.3 %Yellowstone County86.3Silver Bow County: 84.9 %Silver Bow County84.9Sanders County: 82 %Sanders County82Missoula County: 81.6 %Missoula County81.6Richland County: 79.5 %Richland County79.5Ravalli County: 79.2 %Ravalli County79.2Flathead County: 73.7 %Flathead County73.7Lewis and Clark County: 71.5 %Lewis and Clark County71.5Lincoln County: 54.4 %Lincoln County54.4
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2025 (%)Change on 2024
1Gallatin County98.1+8 pts
2Rosebud County98+1.6 pts
3Teton County97.1+4.8 pts
4Lake County96.8+2.9 pts
5Beaverhead County94.7+8.6 pts
5Powell County94.7+6.1 pts
7Hill County92.1-0.5 pts
8Glacier County91.7+3.3 pts
9Phillips County91.4+2.2 pts
10Fergus County90.7+5.5 pts
11Dawson County90.3+0.4 pts
12Custer County87.2-3.7 pts
12Roosevelt County87.2-1.6 pts
14Sheridan County86.8-0.6 pts
15Yellowstone County86.3+10.1 pts
16Silver Bow County84.9+14.4 pts
17Sanders County82-11.1 pts
18Missoula County81.6+16.8 pts
19Richland County79.5-4.4 pts
20Ravalli County79.2+9 pts
21Flathead County73.7+4.6 pts
22Lewis and Clark County71.5+7.8 pts
23Lincoln County54.4+3.7 pts

Other periods

About this ranking

Days with a daily Air Quality Index of 0 to 50 (good) as a percentage of the days of the year with an AQI in a US county. Calculated by Invokely from the day counts in the EPA AirData annual summaries; both counts are stored with each value.

United States counties with air quality monitors only, about 1,000 of some 3,100 in recent years; a county without monitors has no value. The number of days with an AQI differs between counties because some monitors run only in the ozone season.

Every value in the ranking comes from the same publisher and the same period, so the counties are compared on one definition. 13 counties with data in other periods have no value for 2025 and are left out rather than filled from another source. Equal values share a rank.

How to cite

U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.

Citation styles

The publisher is the author. Invokely is named only as the place the figures were read, where a style asks for it.

APA 7

U.S. Environmental Protection Agency. (2026). EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts (Counties in Montana by share of days with good air quality (US EPA AQI), 2025) [Data set]. Retrieved October 12, 2026, from https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual

MLA 9

EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts, Counties in Montana by share of days with good air quality (US EPA AQI), 2025. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/good-air-quality-days-share/montana-counties. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. Counties in Montana by share of days with good air quality (US EPA AQI), 2025. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/good-air-quality-days-share/montana-counties.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts, Counties in Montana by share of days with good air quality (US EPA AQI), 2025 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/good-air-quality-days-share/montana-counties (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_montana_by_2025,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts: Counties in Montana by share of days with good air quality (US EPA AQI), 2025}},
  year = {2026},
  howpublished = {Data set},
  url = {https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual},
  urldate = {2026-10-12},
  note = {Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/montana-counties. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. https://aqs.epa.gov/aqsweb/airdata/download\_files.html\#Annual. Retrieved 2026-10-12.},
}
RIS
TY  - DATA
AU  - U.S. Environmental Protection Agency
TI  - EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts: Counties in Montana by share of days with good air quality (US EPA AQI), 2025
PY  - 2026
DA  - 2026/07/13
PB  - U.S. Environmental Protection Agency
DB  - Invokely
UR  - https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual
L2  - https://invokely.ai/rankings/good-air-quality-days-share/montana-counties
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/montana-counties.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
ER  -
Embed this chart

Paste this code into a web page or a blog post. The chart shows the latest figures as they are published, with the source and a link back to this page.

Sites that read oEmbed links, such as WordPress, can show the chart when you paste the link to this page.

Use this data in your AI agent

Invokely serves this figure to AI assistants through MCP and to code through a REST API, with the source and citation attached. Ask your assistant:

Rank Counties in Montana by share of days with good air quality (US EPA AQI) using official data, and cite the source.
rank_places {"indicator":"aqi_good_days_share","level":"province","within":"Montana","limit":10}
GET https://invokely.ai/api/v1/rank?indicator=aqi_good_days_share&level=province&within=Montana&limit=10

Connect Claude, ChatGPT or Cursor in one step. The trial answers 25 calls a day without an account.

Questions

Which county has the highest share of days with good air quality (US EPA AQI)?

Gallatin County, with 98.1% in 2025, according to EPA.

Which county has the lowest share of days with good air quality (US EPA AQI)?

Lincoln County, with 54.4% in 2025.

Where does this ranking come from?

Every value comes from one source and one period, so the places are comparable: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. Retrieved 2026-10-12. 13 counties have no value for 2025 and are not ranked.

Share of days with good air quality (US EPA AQI): other rankings

Counties in Montana: more rankings