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), 1002 monitored counties and 504 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)

Counties are ranked on a full record: at least 100 monitored days in the 2025 release. A county with a shorter or older record is marked and listed after the ranked ones.

# County Good days Median AQI Category
1 Karnes County, Texas 100.0% 6 Good
2 Wilson County, Texas 100.0% 8 Good
3 Carbon County, Wyoming 100.0% 8 Good
4 Kenai Peninsula County, Alaska 100.0% 9 Good
5 Sonoma County, California 100.0% 9 Good
6 Uinta County, Wyoming 100.0% 9 Good
7 Martin County, North Carolina 100.0% 31 Good
8 Pacific County, Washington 99.7% 16 Good
9 Denali County, Alaska 99.7% 33 Good
10 Navajo County, Arizona 99.5% 13 Good
11 Lake County, California 99.2% 31 Good
12 Solano County, California 99.2% 33 Good
13 Lincoln County, Wyoming 98.9% 10 Good
14 Taos County, New Mexico 98.9% 16 Good
15 Liberty County, Florida 98.5% 33 Good
16 Gallatin County, Montana 98.1% 11 Good
17 Flagler County, Florida 98.1% 34 Good
18 Maui County, Hawaii 98.1% 21 Good
19 Park County, Wyoming 98.0% 13 Good
20 Elmore County, Alabama 97.9% 34 Good
21 Prince Edward County, Virginia 97.8% 33 Good
22 Mayagnez County, Puerto Rico 97.8% 9 Good
23 Knox County, Maine 97.8% 33 Good
24 Fauquier County, Virginia 97.5% 34 Good
25 Lenoir County, North Carolina 97.5% 35 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. A county monitored fewer than 100 days is marked Limited sample and listed after the counties that clear that floor, because a short record can show a perfect share that one bad reading would erase.
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.

Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files · 2020–2025

Every figure on PlainAirData 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. Data current as of 2025.

Informational only, not professional advice. Data from EPA AQS. See our disclaimer.