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 23 counties in 2023, at 97.9%. Lincoln County had the lowest, at 41.5%. The median was 79.4%. Source: EPA.

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Highest97.9Rosebud County
Lowest41.5Lincoln County
Median79.423 counties

Map of counties, 2023

Beaverhead County: 96.1 %Cascade County: 50.1 %Custer County: 79.1 %Fergus County: 86.5 %Flathead County: 64.9 %Gallatin County: 90.7 %Glacier County: 89 %Hill County: 79.4 %Lake County: 92.7 %Lewis and Clark County: 65.8 %Lincoln County: 41.5 %Missoula County: 42.9 %Phillips County: 79.4 %Powder River County: 68.7 %Powell County: 91.7 %Ravalli County: 80.7 %Richland County: 73.4 %Roosevelt County: 86.1 %Rosebud County: 97.9 %Sanders County: 72.3 %Sheridan County: 85.7 %Silver Bow County: 73.4 %Yellowstone County: 85.7 %
  • Under 67
  • 67 to 78
  • 78 to 86
  • 86 to 90
  • 90 and over
  • No data
%, 2023. 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, 2023

Rosebud County: 97.9 %Rosebud County97.9Beaverhead County: 96.1 %Beaverhead County96.1Lake County: 92.7 %Lake County92.7Powell County: 91.7 %Powell County91.7Gallatin County: 90.7 %Gallatin County90.7Glacier County: 89 %Glacier County89Fergus County: 86.5 %Fergus County86.5Roosevelt County: 86.1 %Roosevelt County86.1Sheridan County: 85.7 %Sheridan County85.7Yellowstone County: 85.7 %Yellowstone County85.7Ravalli County: 80.7 %Ravalli County80.7Hill County: 79.4 %Hill County79.4Phillips County: 79.4 %Phillips County79.4Custer County: 79.1 %Custer County79.1Richland County: 73.4 %Richland County73.4Silver Bow County: 73.4 %Silver Bow County73.4Sanders County: 72.3 %Sanders County72.3Powder River County: 68.7 %Powder River County68.7Lewis and Clark County: 65.8 %Lewis and Clark County65.8Flathead County: 64.9 %Flathead County64.9Cascade County: 50.1 %Cascade County50.1Missoula County: 42.9 %Missoula County42.9Lincoln County: 41.5 %Lincoln County41.5Rosebud County: 97.9 %Rosebud County97.9Beaverhead County: 96.1 %Beaverhead County96.1Lake County: 92.7 %Lake County92.7Powell County: 91.7 %Powell County91.7Gallatin County: 90.7 %Gallatin County90.7Glacier County: 89 %Glacier County89Fergus County: 86.5 %Fergus County86.5Roosevelt County: 86.1 %Roosevelt County86.1Sheridan County: 85.7 %Sheridan County85.7Yellowstone County: 85.7 %Yellowstone County85.7Ravalli County: 80.7 %Ravalli County80.7Hill County: 79.4 %Hill County79.4Phillips County: 79.4 %Phillips County79.4Custer County: 79.1 %Custer County79.1Richland County: 73.4 %Richland County73.4Silver Bow County: 73.4 %Silver Bow County73.4Sanders County: 72.3 %Sanders County72.3Powder River County: 68.7 %Powder River County68.7Lewis and Clark County: 65.8 %Lewis and Clark County65.8Flathead County: 64.9 %Flathead County64.9Cascade County: 50.1 %Cascade County50.1Missoula County: 42.9 %Missoula County42.9Lincoln County: 41.5 %Lincoln County41.5
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2023 (%)Change on 2022
1Rosebud County97.9-2.1 pts
2Beaverhead County96.1n/a
3Lake County92.7-3.2 pts
4Powell County91.7-0.4 pts
5Gallatin County90.7+11.2 pts
6Glacier County89n/a
7Fergus County86.5-6.9 pts
8Roosevelt County86.1-10.9 pts
9Sheridan County85.7-9.8 pts
9Yellowstone County85.7+1.6 pts
11Ravalli County80.7+1.6 pts
12Hill County79.4n/a
12Phillips County79.4-14.8 pts
14Custer County79.1-8.3 pts
15Richland County73.4-15.8 pts
15Silver Bow County73.40 pts
17Sanders County72.3-0.6 pts
18Powder River County68.7-11.3 pts
19Lewis and Clark County65.8+0.3 pts
20Flathead County64.9-3.3 pts
21Cascade County50.1-39.9 pts
22Missoula County42.9+2.1 pts
23Lincoln County41.5-8.9 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 2023 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), 2023) [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), 2023. 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=2023. 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), 2023. 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=2023.

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), 2023 [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=2023 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_montana_by_2023,
  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), 2023}},
  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=2023. 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), 2023
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=2023
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/montana-counties?period=2023.
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 97.9% in 2023, according to EPA.

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

Lincoln County, with 41.5% in 2023.

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 2023 and are not ranked.

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

Counties in Montana: more rankings