Air quality tool

Cleanest Counties Finder

Filter U.S. counties by state and rank them by their share of Good air days, then open any county for the full picture.

According to the U.S. Environmental Protection Agency (EPA), 977 monitored counties and 496 metro areas reported Air Quality Index readings through the federal Air Quality System (AQS) for the 2025 reporting year. This tool reads those official records directly; see the methodology for how every figure is computed.

Cleanest counties nationwide (25)

# County Good days Median AQI Category
1 Lawrence County, Alabama 100.0% 23 Good
2 Denali County, Alaska 100.0% 38 Good
3 Kenai Peninsula County, Alaska 100.0% 8 Good
4 North Slope County, Alaska 100.0% 7 Good
5 Lake County, California 100.0% 17 Good
6 Marin County, California 100.0% 21 Good
7 Siskiyou County, California 100.0% 6 Good
8 Sonoma County, California 100.0% 9 Good
9 Jackson County, Colorado 100.0% 3 Good
10 San Juan County, Colorado 100.0% 4 Good
11 Custer County, Idaho 100.0% 3 Good
12 Keweenaw County, Michigan 100.0% 7 Good
13 Cook County, Minnesota 100.0% 12 Good
14 Stoddard County, Missouri 100.0% 21 Good
15 Taney County, Missouri 100.0% 26 Good
16 Beaverhead County, Montana 100.0% 12 Good
17 Lake County, Montana 100.0% 4 Good
18 Powell County, Montana 100.0% 6 Good
19 Roosevelt County, Montana 100.0% 9 Good
20 Rosebud County, Montana 100.0% 4 Good
21 Sanders County, Montana 100.0% 15 Good
22 Sheridan County, Montana 100.0% 13 Good
23 Catron County, New Mexico 100.0% 8 Good
24 Los Alamos County, New Mexico 100.0% 10 Good
25 Socorro County, New Mexico 100.0% 12 Good

More ways to explore

AQI lookupSearch a single county’s air quality. Compare countiesPut counties side by side. AQI health calculatorWhat an AQI value means for health. Cleanest-air rankingsNational good-day rankings. Browse by stateState summaries and county lists. MethodologyHow good-day share is built.

Frequently asked questions

How does the cleanest counties finder work?
Choose a state, or leave it on all states, and the tool ranks the matching counties by their share of Good air days from EPA Air Quality System data. Switch the order to surface either the cleanest or the most polluted counties. Each result links to a full county profile.
What is a Good air day?
A Good day is any monitored day with an Air Quality Index of 50 or below, the cleanest band on the EPA scale. Ranking by the share of Good days lets a heavily monitored county and a lightly monitored one compare fairly, because it is a percentage rather than a raw count.
Why might my state show only a few counties?
The EPA places monitors where population, emissions, or attainment status warrant them, so rural states can have only a handful of monitored counties. The finder ranks exactly the counties with an active monitor; unmonitored counties are not estimated.

Every figure on PlainAir is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.