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)

Rosebud County had the highest share of days with good air quality (US EPA AQI) of 24 counties in 2024, at 96.4%. Lincoln County had the lowest, at 50.7%. The median was 87.9%. Source: EPA.

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Highest96.4Rosebud County
Lowest50.7Lincoln County
Median87.924 counties

Map of counties, 2024

Beaverhead County: 86.1 %Cascade County: 59.8 %Custer County: 90.9 %Dawson County: 89.9 %Fergus County: 85.2 %Flathead County: 69.1 %Gallatin County: 90.1 %Glacier County: 88.4 %Hill County: 92.6 %Lake County: 93.9 %Lewis and Clark County: 63.7 %Lincoln County: 50.7 %Missoula County: 64.8 %Phillips County: 89.2 %Powell County: 88.6 %Ravalli County: 70.2 %Richland County: 83.9 %Roosevelt County: 88.8 %Rosebud County: 96.4 %Sanders County: 93.1 %Sheridan County: 87.4 %Silver Bow County: 70.5 %Teton County: 92.3 %Yellowstone County: 76.2 %
  • Under 70
  • 70 to 85
  • 85 to 89
  • 89 to 91
  • 91 and over
  • No data
%, 2024. 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, 2024

Rosebud County: 96.4 %Rosebud County96.4Lake County: 93.9 %Lake County93.9Sanders County: 93.1 %Sanders County93.1Hill County: 92.6 %Hill County92.6Teton County: 92.3 %Teton County92.3Custer County: 90.9 %Custer County90.9Gallatin County: 90.1 %Gallatin County90.1Dawson County: 89.9 %Dawson County89.9Phillips County: 89.2 %Phillips County89.2Roosevelt County: 88.8 %Roosevelt County88.8Powell County: 88.6 %Powell County88.6Glacier County: 88.4 %Glacier County88.4Sheridan County: 87.4 %Sheridan County87.4Beaverhead County: 86.1 %Beaverhead County86.1Fergus County: 85.2 %Fergus County85.2Richland County: 83.9 %Richland County83.9Yellowstone County: 76.2 %Yellowstone County76.2Silver Bow County: 70.5 %Silver Bow County70.5Ravalli County: 70.2 %Ravalli County70.2Flathead County: 69.1 %Flathead County69.1Missoula County: 64.8 %Missoula County64.8Lewis and Clark County: 63.7 %Lewis and Clark County63.7Cascade County: 59.8 %Cascade County59.8Lincoln County: 50.7 %Lincoln County50.7Rosebud County: 96.4 %Rosebud County96.4Lake County: 93.9 %Lake County93.9Sanders County: 93.1 %Sanders County93.1Hill County: 92.6 %Hill County92.6Teton County: 92.3 %Teton County92.3Custer County: 90.9 %Custer County90.9Gallatin County: 90.1 %Gallatin County90.1Dawson County: 89.9 %Dawson County89.9Phillips County: 89.2 %Phillips County89.2Roosevelt County: 88.8 %Roosevelt County88.8Powell County: 88.6 %Powell County88.6Glacier County: 88.4 %Glacier County88.4Sheridan County: 87.4 %Sheridan County87.4Beaverhead County: 86.1 %Beaverhead County86.1Fergus County: 85.2 %Fergus County85.2Richland County: 83.9 %Richland County83.9Yellowstone County: 76.2 %Yellowstone County76.2Silver Bow County: 70.5 %Silver Bow County70.5Ravalli County: 70.2 %Ravalli County70.2Flathead County: 69.1 %Flathead County69.1Missoula County: 64.8 %Missoula County64.8Lewis and Clark County: 63.7 %Lewis and Clark County63.7Cascade County: 59.8 %Cascade County59.8Lincoln County: 50.7 %Lincoln County50.7
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2024 (%)Change on 2023
1Rosebud County96.4-1.5 pts
2Lake County93.9+1.2 pts
3Sanders County93.1+20.8 pts
4Hill County92.6+13.2 pts
5Teton County92.3n/a
6Custer County90.9+11.8 pts
7Gallatin County90.1-0.6 pts
8Dawson County89.9n/a
9Phillips County89.2+9.8 pts
10Roosevelt County88.8+2.7 pts
11Powell County88.6-3.1 pts
12Glacier County88.4-0.6 pts
13Sheridan County87.4+1.7 pts
14Beaverhead County86.1-10 pts
15Fergus County85.2-1.3 pts
16Richland County83.9+10.5 pts
17Yellowstone County76.2-9.5 pts
18Silver Bow County70.5-2.9 pts
19Ravalli County70.2-10.5 pts
20Flathead County69.1+4.2 pts
21Missoula County64.8+21.9 pts
22Lewis and Clark County63.7-2.1 pts
23Cascade County59.8+9.7 pts
24Lincoln County50.7+9.2 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. 12 counties with data in other periods have no value for 2024 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), 2024) [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), 2024. 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?period=2024. 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), 2024. 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?period=2024.

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), 2024 [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?period=2024 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_montana_by_2024,
  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), 2024}},
  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?period=2024. 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), 2024
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?period=2024
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/montana-counties?period=2024.
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  -
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Questions

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

Rosebud County, with 96.4% in 2024, according to EPA.

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

Lincoln County, with 50.7% in 2024.

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. 12 counties have no value for 2024 and are not ranked.

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

Counties in Montana: more rankings