Counties in Oregon by highest daily Air Quality Index (US EPA)

Marion County had the highest highest daily Air Quality Index (US EPA) of 23 counties in 2020, at 1,272. Lake County had the lowest, at 166. The median was 738. Source: the U.S. Environmental Protection Agency.

Highest1,272Marion County

Lowest166Lake County

Median73823 counties

Map of counties, 2020

Under 340
340 to 580
580 to 770
770 to 960
960 and over
No data

index, 2020. Hatched areas have no value for this period. Source: EPA, EPA AirData annual AQI by county: highest daily AQI. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2020

index. Source: EPA, EPA AirData annual AQI by county: highest daily AQI. Retrieved 2026-10-12.

Full ranking

Rank	Counties	2020 index	Change on 2019
1	Marion County	1,272	+1,179
2	Jefferson County	1,135	+1,013
3	Deschutes County	1,099	+945
4	Crook County	1,033	+930
5	Lane County	1,000	+883
6	Douglas County	902	+820
7	Jackson County	900	+710
8	Linn County	853	+749
9	Multnomah County	779	+688
10	Josephine County	763	+588
10	Klamath County	763	+637
12	Umatilla County	738	+634
13	Wasco County	599	+510
14	Washington County	595	+493
15	Benton County	541	+454
16	Clackamas County	481	+380
17	Grant County	393	+290
18	Harney County	357	+226
19	Union County	326	+238
20	Columbia County	293	+209
21	Baker County	225	+157
22	Wallowa County	222	+119
23	Lake County	166	+60

Other periods

About this ranking

Highest daily Air Quality Index (AQI) value recorded in a US county during the year, from the EPA AirData annual summaries. Values above 500 are beyond the AQI scale and are published as EPA computes them.

A single day decides the value, so one wildfire or dust event can set it. Dust from the dry Owens Lake bed puts Inyo and Mono counties in California in the thousands. 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. 3 counties with data in other periods have no value for 2020 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: highest 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: highest daily AQI (Counties in Oregon by highest daily Air Quality Index (US EPA), 2020) [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: highest daily AQI, Counties in Oregon by highest daily Air Quality Index (US EPA), 2020. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/highest-daily-air-quality-index/oregon-counties?period=2020. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: highest daily AQI. Counties in Oregon by highest daily Air Quality Index (US EPA), 2020. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/highest-daily-air-quality-index/oregon-counties?period=2020.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: highest daily AQI, Counties in Oregon by highest daily Air Quality Index (US EPA), 2020 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/highest-daily-air-quality-index/oregon-counties?period=2020 (Accessed: 12 October 2026).

BibTeX

@misc{environmental_counties_in_oregon_by_2020,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: highest daily AQI: Counties in Oregon by highest daily Air Quality Index (US EPA), 2020}},
  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/highest-daily-air-quality-index/oregon-counties?period=2020. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: highest 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: highest daily AQI: Counties in Oregon by highest daily Air Quality Index (US EPA), 2020
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/highest-daily-air-quality-index/oregon-counties?period=2020
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/highest-daily-air-quality-index/oregon-counties?period=2020.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: highest daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
ER  -

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Rank Counties in Oregon by highest daily Air Quality Index (US EPA) using official data, and cite the source.

rank_places {"indicator":"aqi_max","level":"province","within":"Oregon","limit":10}
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Questions

Which county has the highest highest daily Air Quality Index (US EPA)?

Marion County, with 1,272 in 2020, according to the U.S. Environmental Protection Agency.

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

Lake County, with 166 in 2020.

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: highest daily AQI. Retrieved 2026-10-12. 3 counties have no value for 2020 and are not ranked.