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

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

Gem County had the highest median Air Quality Index (US EPA) of 24 counties in 2004, at 62. Custer County had the lowest, at 13. The median was 34. Source: the U.S. Environmental Protection Agency.

Keep it in a collection in your library.
Highest62Gem County
Lowest13Custer County
Median3424 counties

Map of counties, 2004

Ada County: 44 indexBannock County: 18 indexBenewah County: 43 indexBingham County: 19 indexBoise County: 33 indexBonner County: 13 indexBonneville County: 34 indexBoundary County: 28 indexButte County: 44 indexCanyon County: 44 indexCaribou County: 27 indexCuster County: 13 indexElmore County: 42 indexFranklin County: 51 indexGem County: 62 indexIdaho County: 26 indexKootenai County: 51 indexLatah County: 26 indexLemhi County: 29 indexNez Perce County: 33 indexPower County: 49 indexShoshone County: 46 indexTwin Falls County: 36 indexValley County: 34 index
  • Under 26
  • 26 to 33
  • 33 to 41
  • 41 to 45
  • 45 and over
  • No data
index, 2004. 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, 2004

Gem County: 62 indexGem County62Franklin County: 51 indexFranklin County51Kootenai County: 51 indexKootenai County51Power County: 49 indexPower County49Shoshone County: 46 indexShoshone County46Ada County: 44 indexAda County44Butte County: 44 indexButte County44Canyon County: 44 indexCanyon County44Benewah County: 43 indexBenewah County43Elmore County: 42 indexElmore County42Twin Falls County: 36 indexTwin Falls County36Bonneville County: 34 indexBonneville County34Valley County: 34 indexValley County34Boise County: 33 indexBoise County33Nez Perce County: 33 indexNez Perce County33Lemhi County: 29 indexLemhi County29Boundary County: 28 indexBoundary County28Caribou County: 27 indexCaribou County27Idaho County: 26 indexIdaho County26Latah County: 26 indexLatah County26Bingham County: 19 indexBingham County19Bannock County: 18 indexBannock County18Bonner County: 13 indexBonner County13Custer County: 13 indexCuster County13Gem County: 62 indexGem County62Franklin County: 51 indexFranklin County51Kootenai County: 51 indexKootenai County51Power County: 49 indexPower County49Shoshone County: 46 indexShoshone County46Ada County: 44 indexAda County44Butte County: 44 indexButte County44Canyon County: 44 indexCanyon County44Benewah County: 43 indexBenewah County43Elmore County: 42 indexElmore County42Twin Falls County: 36 indexTwin Falls County36Bonneville County: 34 indexBonneville County34Valley County: 34 indexValley County34Boise County: 33 indexBoise County33Nez Perce County: 33 indexNez Perce County33Lemhi County: 29 indexLemhi County29Boundary County: 28 indexBoundary County28Caribou County: 27 indexCaribou County27Idaho County: 26 indexIdaho County26Latah County: 26 indexLatah County26Bingham County: 19 indexBingham County19Bannock County: 18 indexBannock County18Bonner County: 13 indexBonner County13Custer County: 13 indexCuster County13
index. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Retrieved 2026-10-12.

Full ranking

RankCounties2004
index		Change on 2003
1Gem County62n/a
2Franklin County51n/a
2Kootenai County51+13
4Power County49+3
5Shoshone County46+26
6Ada County44+4
6Butte County44+1
6Canyon County44+1
9Benewah County43+6
10Elmore County42+4
11Twin Falls County36+6
12Bonneville County34+5
12Valley County340
14Boise County33-1
14Nez Perce County33+1
16Lemhi County29+5
17Boundary County28+10
18Caribou County27+3
19Idaho County26-13
19Latah County26+4
21Bingham County19-10
22Bannock County18-1
23Bonner County13-1
23Custer County13+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. 7 counties with data in other periods have no value for 2004 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), 2004) [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), 2004. 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?period=2004. 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), 2004. 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?period=2004.

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), 2004 [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?period=2004 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_idaho_by_2004,
  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), 2004}},
  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?period=2004. 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), 2004
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?period=2004
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/median-air-quality-index/idaho-counties?period=2004.
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)?

Gem County, with 62 in 2004, according to the U.S. Environmental Protection Agency.

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

Custer County, with 13 in 2004.

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. 7 counties have no value for 2004 and are not ranked.

Median Air Quality Index (US EPA): other rankings

Counties in Idaho: more rankings