Data / Rankings / Median Air Quality Index (US EPA) / Counties in Idaho

Counties in Idaho by median Air Quality Index (US EPA), 2005

Kootenai County had the highest median Air Quality Index (US EPA) of 23 counties in 2005, at 51. Custer County had the lowest, at 11. The median was 36. Source: the U.S. Environmental Protection Agency.

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Highest51Kootenai County
Lowest11Custer County
Median3623 counties

Map of counties, 2005

Ada County: 44 indexBannock County: 19 indexBenewah County: 38 indexBingham County: 19 indexBoise County: 43 indexBonner County: 14 indexBonneville County: 27 indexBoundary County: 28 indexButte County: 11 indexCanyon County: 44 indexCuster County: 11 indexElmore County: 47 indexFranklin County: 31 indexGem County: 38 indexIdaho County: 22 indexKootenai County: 51 indexLatah County: 20 indexLemhi County: 38 indexNez Perce County: 27 indexPower County: 50 indexShoshone County: 48 indexTwin Falls County: 36 indexValley County: 39 index
  • Under 19
  • 19 to 28
  • 28 to 38
  • 38 to 44
  • 44 and over
  • No data
index, 2005. Hatched areas have no value for this period. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2005

Kootenai County: 51 indexKootenai County51Power County: 50 indexPower County50Shoshone County: 48 indexShoshone County48Elmore County: 47 indexElmore County47Ada County: 44 indexAda County44Canyon County: 44 indexCanyon County44Boise County: 43 indexBoise County43Valley County: 39 indexValley County39Benewah County: 38 indexBenewah County38Gem County: 38 indexGem County38Lemhi County: 38 indexLemhi County38Twin Falls County: 36 indexTwin Falls County36Franklin County: 31 indexFranklin County31Boundary County: 28 indexBoundary County28Bonneville County: 27 indexBonneville County27Nez Perce County: 27 indexNez Perce County27Idaho County: 22 indexIdaho County22Latah County: 20 indexLatah County20Bannock County: 19 indexBannock County19Bingham County: 19 indexBingham County19Bonner County: 14 indexBonner County14Butte County: 11 indexButte County11Custer County: 11 indexCuster County11Kootenai County: 51 indexKootenai County51Power County: 50 indexPower County50Shoshone County: 48 indexShoshone County48Elmore County: 47 indexElmore County47Ada County: 44 indexAda County44Canyon County: 44 indexCanyon County44Boise County: 43 indexBoise County43Valley County: 39 indexValley County39Benewah County: 38 indexBenewah County38Gem County: 38 indexGem County38Lemhi County: 38 indexLemhi County38Twin Falls County: 36 indexTwin Falls County36Franklin County: 31 indexFranklin County31Boundary County: 28 indexBoundary County28Bonneville County: 27 indexBonneville County27Nez Perce County: 27 indexNez Perce County27Idaho County: 22 indexIdaho County22Latah County: 20 indexLatah County20Bannock County: 19 indexBannock County19Bingham County: 19 indexBingham County19Bonner County: 14 indexBonner County14Butte County: 11 indexButte County11Custer County: 11 indexCuster County11
index. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Retrieved 2026-10-12.

Full ranking

RankCounties2005
index		Change on 2004
1Kootenai County510
2Power County50+1
3Shoshone County48+2
4Elmore County47+5
5Ada County440
5Canyon County440
7Boise County43+10
8Valley County39+5
9Benewah County38-5
9Gem County38-24
9Lemhi County38+9
12Twin Falls County360
13Franklin County31-20
14Boundary County280
15Bonneville County27-7
15Nez Perce County27-6
17Idaho County22-4
18Latah County20-6
19Bannock County19+1
19Bingham County190
21Bonner County14+1
22Butte County11-33
22Custer County11-2

Other periods

About this ranking

Median of the daily Air Quality Index (AQI) values of a US county over the days of the year with an AQI, from the EPA AirData annual summaries.

More on how it is measured
  • The daily county AQI is the highest AQI among the monitors and pollutants reported that day (ozone, PM2.5, PM10, carbon monoxide and nitrogen dioxide).
  • Lower is cleaner: 0 to 50 is good, 51 to 100 moderate and above 100 unhealthy for sensitive groups.

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. 8 counties with data in other periods have no value for 2005 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: median daily AQI. 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: median daily AQI (Counties in Idaho by median Air Quality Index (US EPA), 2005) [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: median daily AQI, Counties in Idaho by median Air Quality Index (US EPA), 2005. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/median-air-quality-index/idaho-counties. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: median daily AQI. Counties in Idaho by median Air Quality Index (US EPA), 2005. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/median-air-quality-index/idaho-counties.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: median daily AQI, Counties in Idaho by median Air Quality Index (US EPA), 2005 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/median-air-quality-index/idaho-counties (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_idaho_by_2005,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: median daily AQI: Counties in Idaho by median Air Quality Index (US EPA), 2005}},
  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/median-air-quality-index/idaho-counties. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. 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: median daily AQI: Counties in Idaho by median Air Quality Index (US EPA), 2005
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/median-air-quality-index/idaho-counties
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/median-air-quality-index/idaho-counties.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. 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 median Air Quality Index (US EPA)?

Kootenai County, with 51 in 2005, according to the U.S. Environmental Protection Agency.

Which county has the lowest median Air Quality Index (US EPA)?

Custer County, with 11 in 2005.

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: median daily AQI. Retrieved 2026-10-12. 8 counties have no value for 2005 and are not ranked.

Median Air Quality Index (US EPA): other rankings

Counties in Idaho: more rankings