National ranking · cleanest air

Best Air Quality in the US (2025)

Ranked by the highest share of Good air days among counties with at least 100 monitored days in 2025, the counties where residents breathe the cleanest air most often, from EPA Air Quality System monitoring.

Compiled by PlainAirData · August 23, 2026

100.0%
#1 Carbon, Wyoming: 17
Counties ranked

Carbon County, Wyoming leads the 2025 cleanest-air list among 17 ranked U.S. counties (100.0% Good)

According to the U.S. EPA Air Quality System, this ranking orders 17 counties with at least 100 monitored days in 2025 by the highest share of days in the Good AQI band, using median AQI to separate near-ties. It describes a historical reporting year, not today's air quality. For current conditions and alerts, use AirNow.

Data source EPA Air Quality System (AQS)

#1 Good-day share: Carbon County, Wyoming ranks #1 of 17 for Good-day share at 100.0% (2 counties tied at 100% Good; median AQI breaks ties).
#1 median AQI: #1 median AQI: 8
Counties ranked: Counties ranked: 17
Tied at 100% Good: Tied at 100% Good: 2

Data updated August 2026 from the compiled EPA AQS release in this database.

Counties below the 100-day monitoring floor are excluded: with only a handful of readings, a single clean stretch can push a county to a 100% Good-day rate that a normal year's weather would not hold up. 2 counties tie at 100.0% with this floor applied, all with a genuinely large sample of monitored days. For comparison, the cohort median across all 951 floor-qualifying counties is 77.5%, meaning the difference between a top-ranked county and a typical monitored county is real, not sampling noise.

Filter this ranking

Filters keep the Good-day-share ranking contract. A state filter ranks that state's qualifying counties; pollutant filters keep rows whose annual day-type count is led by ozone, PM2.5, or PM10. Raising the monitored-days floor tightens the sample beyond the default 100-day Module-34 guard.

Showing 17 matching Wyoming counties . Back to the national top 50.

Where the national cleanest cohort concentrates

Among the unfiltered national top 50 (highest Good-day share, ≥100 monitored days), Virginia contributes 6 counties , followed by Wyoming (4). State filters rank every qualifying county inside one jurisdiction.

Compare any two counties

For a side-by-side annual change view, open the county compare tool.

Cleanest of the clean: lowest median AQI

Among the top counties (all near a 100% Good-day record), the lowest typical AQI. Shorter is cleaner.

Median AQI · EPA Air Quality System

Ranked counties

#	County	State	Good Days %	Median AQI	Good Days	Days Monitored	Day driver
1	Carbon	Wyoming	100.0%	8 Good	362	362	Ozone
2	Uinta	Wyoming	100.0%	9 Good	269	269	PM10
3	Lincoln	Wyoming	98.9%	10 Good	361	365	PM10
4	Park	Wyoming	98.0%	13 Good	348	355	PM2.5
5	Washakie	Wyoming	96.3%	8 Good	342	355	PM2.5
6	Converse	Wyoming	96.2%	40 Good	351	365	Ozone
7	Johnson	Wyoming	92.8%	41 Good	337	363	Ozone
8	Platte	Wyoming	90.6%	15 Good	327	361	PM10
9	Sheridan	Wyoming	89.1%	27 Good	320	359	PM2.5
10	Natrona	Wyoming	86.3%	42 Good	315	365	Ozone
11	Teton	Wyoming	84.9%	44 Good	310	365	Ozone
12	Laramie	Wyoming	75.1%	45 Good	274	365	Ozone
13	Campbell	Wyoming	74.3%	44 Good	271	365	Ozone
14	Sweetwater	Wyoming	72.9%	44 Good	266	365	Ozone
15	Sublette	Wyoming	70.1%	47 Good	256	365	Ozone
16	Fremont	Wyoming	69.6%	47 Good	254	365	Ozone
17	Albany	Wyoming	55.6%	49 Good	203	365	Ozone

Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS). Good Days % is the share of monitored days with AQI at or below 50. Counties ranked by good_pct descending

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.