Data / Share of days with good air quality (US EPA AQI) / Flathead County

Share of days with good air quality (US EPA AQI) in Flathead County

Share of days with good air quality (US EPA AQI) in Flathead County was 73.7% in 2025, according to EPA. That is up 4.6 pts from 2024. That is the 21st highest of 23 counties in 2025.

202573.7%
Change on 2024+4.6 pts
Rank21st of 23Counties in Montana ranked
Series high85.81998
Series low33.42009

Next release: Tuesday, 13 July 2027, estimated by Invokely from past publication dates (low confidence), not announced by the publisher. Release calendar

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Share of days with good air quality (US EPA AQI) in Flathead County, 1985 to 2025

2040608010019851991199720032009201520251985: 71.1 %1986: 50.8 %1987: 59 %1988: 71.7 %1989: 80.7 %1990: 81.6 %1991: 77 %1992: 77.2 %1993: 82.2 %1994: 74.8 %1995: 84.1 %1996: 80.3 %1997: 85.2 %1998: 85.8 %1999: 73.2 %2000: 75.4 %2001: 85.5 %2002: 83 %2003: 74.2 %2004: 78.4 %2005: 77.3 %2006: 77 %2007: 74 %2008: 57.1 %2009: 33.4 %2010: 51.5 %2011: 60.5 %2012: 70.5 %2013: 64.4 %2014: 69.6 %2015: 59.2 %2016: 81.4 %2017: 68.5 %2018: 60.8 %2019: 73.2 %2020: 78.1 %2021: 73.4 %2022: 68.2 %2023: 64.9 %2024: 69.1 %2025: 73.7 %2040608010019851999201320251985: 71.1 %1986: 50.8 %1987: 59 %1988: 71.7 %1989: 80.7 %1990: 81.6 %1991: 77 %1992: 77.2 %1993: 82.2 %1994: 74.8 %1995: 84.1 %1996: 80.3 %1997: 85.2 %1998: 85.8 %1999: 73.2 %2000: 75.4 %2001: 85.5 %2002: 83 %2003: 74.2 %2004: 78.4 %2005: 77.3 %2006: 77 %2007: 74 %2008: 57.1 %2009: 33.4 %2010: 51.5 %2011: 60.5 %2012: 70.5 %2013: 64.4 %2014: 69.6 %2015: 59.2 %2016: 81.4 %2017: 68.5 %2018: 60.8 %2019: 73.2 %2020: 78.1 %2021: 73.4 %2022: 68.2 %2023: 64.9 %2024: 69.1 %2025: 73.7 %
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12, published 2026-07-13.
All 41 values
Period%
202573.7
202469.1
202364.9
202268.2
202173.4
202078.1
201973.2
201860.8
201768.5
201681.4
201559.2
201469.6
201364.4
201270.5
201160.5
201051.5
200933.4
200857.1
200774
200677
200577.3
200478.4
200374.2
200283
200185.5
200075.4
199973.2
199885.8
199785.2
199680.3
199584.1
199474.8
199382.2
199277.2
199177
199081.6
198980.7
198871.7
198759
198650.8
198571.1

Flathead County compared with nearby places

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
Share of days with good air quality (US EPA AQI), 2025, %. Flathead County is outlined. Same source and period for every area shown. Source: U.S. Environmental Protection Agency. Boundaries: U.S. Census Bureau cartographic boundary files.

Rankings

Definition

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.

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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 (Share of days with good air quality (US EPA AQI), Flathead County, 1985 to 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, Share of days with good air quality (US EPA AQI), Flathead County, 1985 to 2025. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/en/good-air-quality-days-share/flathead-county-montana. 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. Share of days with good air quality (US EPA AQI), Flathead County, 1985 to 2025. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/en/good-air-quality-days-share/flathead-county-montana.

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, Share of days with good air quality (US EPA AQI), Flathead County, 1985 to 2025 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/en/good-air-quality-days-share/flathead-county-montana (Accessed: 12 October 2026).

BibTeX
@misc{environmental_share_of_days_with_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: Share of days with good air quality (US EPA AQI), Flathead County, 1985 to 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/en/good-air-quality-days-share/flathead-county-montana. 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: Share of days with good air quality (US EPA AQI), Flathead County, 1985 to 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/en/good-air-quality-days-share/flathead-county-montana
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/en/good-air-quality-days-share/flathead-county-montana.
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

What is the share of days with good air quality (US EPA AQI) in Flathead County?

Share of days with good air quality (US EPA AQI) in Flathead County was 73.7% in 2025, according to EPA. That is up 4.6 pts from 2024. That is the 21st highest of 23 counties in 2025.

Where does this figure come from?

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 by Invokely on 2026-10-12.

What was the highest share of days with good air quality (US EPA AQI) in Flathead County?

85.8% in 1998, the highest value since 1985 in this series.

Related statistics for Flathead County

All statistics for Flathead County | Flathead County in figures