Data / Rankings / Share of days with good air quality (US EPA AQI) / US counties

US counties by share of days with good air quality (US EPA AQI)

Carroll County had the highest share of days with good air quality (US EPA AQI) of 1008 counties in 2016, at 100%. Hawaii County had the lowest, at 0.5%. The median was 78.2%. Source: EPA.

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Highest100Carroll County
Lowest0.5Hawaii County
Median78.21008 counties

Map of counties, 2016

%, 2016. Hatched areas have no value for this period. Source: Invokely calculation with data from EPA. Boundaries: U.S. Census Bureau cartographic boundary files.

Top 40 counties, 2016

Carroll County: 100 %Carroll County100Columbiana County: 100 %Columbiana County100Dawson County: 100 %Dawson County100Fredericksburg city: 100 %Fredericksburg city100Fremont County: 100 %Fremont County100Garfield County: 100 %Garfield County100Grady County: 100 %Grady County100Hopewell city: 100 %Hopewell city100Horry County: 100 %Horry County100Kenai Peninsula Borough: 100 %Kenai Peninsula Borough100King William County: 100 %King William County100Los Alamos County: 100 %Los Alamos County100Pitkin County: 100 %Pitkin County100Putnam County: 100 %Putnam County100San Juan County: 100 %San Juan County100Union County: 100 %Union County100Wayne County: 100 %Wayne County100Winchester city: 100 %Winchester city100Denali Borough: 99.7 %Denali Borough99.7Franklin County: 99.7 %Franklin County99.7Jerome County: 99.5 %Jerome County99.5Custer County: 99.2 %Custer County99.2Lincoln County: 99.2 %Lincoln County99.2Jackson County: 99.1 %Jackson County99.1Thomas County: 99.1 %Thomas County99.1Georgetown County: 99 %Georgetown County99Socorro County: 99 %Socorro County99Apache County: 98.9 %Apache County98.9Cerro Gordo County: 98.9 %Cerro Gordo County98.9Clark County: 98.9 %Clark County98.9Archuleta County: 98.8 %Archuleta County98.8Elko County: 98.6 %Elko County98.6Muskogee County: 98.6 %Muskogee County98.6Polk County: 98.6 %Polk County98.6Ford County: 98.4 %Ford County98.4Stutsman County: 98.4 %Stutsman County98.4Washington County: 98.4 %Washington County98.4Alamosa County: 98.3 %Alamosa County98.3Aleutians East Borough: 98.3 %Aleutians East Borough98.3Delta County: 98.3 %Delta County98.3Carroll County: 100 %Carroll County100Columbiana County: 100 %Columbiana County100Dawson County: 100 %Dawson County100Fredericksburg city: 100 %Fredericksburg city100Fremont County: 100 %Fremont County100Garfield County: 100 %Garfield County100Grady County: 100 %Grady County100Hopewell city: 100 %Hopewell city100Horry County: 100 %Horry County100Kenai Peninsula Borough: 100 %Kenai Peninsula Borough100King William County: 100 %King William County100Los Alamos County: 100 %Los Alamos County100Pitkin County: 100 %Pitkin County100Putnam County: 100 %Putnam County100San Juan County: 100 %San Juan County100Union County: 100 %Union County100Wayne County: 100 %Wayne County100Winchester city: 100 %Winchester city100Denali Borough: 99.7 %Denali Borough99.7Franklin County: 99.7 %Franklin County99.7Jerome County: 99.5 %Jerome County99.5Custer County: 99.2 %Custer County99.2Lincoln County: 99.2 %Lincoln County99.2Jackson County: 99.1 %Jackson County99.1Thomas County: 99.1 %Thomas County99.1Georgetown County: 99 %Georgetown County99Socorro County: 99 %Socorro County99Apache County: 98.9 %Apache County98.9Cerro Gordo County: 98.9 %Cerro Gordo County98.9Clark County: 98.9 %Clark County98.9Archuleta County: 98.8 %Archuleta County98.8Elko County: 98.6 %Elko County98.6Muskogee County: 98.6 %Muskogee County98.6Polk County: 98.6 %Polk County98.6Ford County: 98.4 %Ford County98.4Stutsman County: 98.4 %Stutsman County98.4Washington County: 98.4 %Washington County98.4Alamosa County: 98.3 %Alamosa County98.3Aleutians East Borough: 98.3 %Aleutians East Borough98.3Delta County: 98.3 %Delta County98.3
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2016 (%)Change on 2015
1Carroll County1000 pts
1Columbiana County1000 pts
1Dawson County100+3.4 pts
1Fredericksburg city1000 pts
1Fremont County1000 pts
1Garfield County100+17.9 pts
1Grady County100n/a
1Hopewell city1000 pts
1Horry County100n/a
1Kenai Peninsula Borough1000 pts
1King William County1000 pts
1Los Alamos County1000 pts
1Pitkin County100+2.4 pts
1Putnam County1000 pts
1San Juan County100+0.8 pts
1Union County100+5.8 pts
1Wayne County100+1.7 pts
1Winchester city1000 pts
19Denali Borough99.7+1.9 pts
19Franklin County99.7+4.5 pts
21Jerome County99.5+8.6 pts
22Custer County99.2-0.8 pts
22Lincoln County99.2+1.9 pts
24Jackson County99.1+4.1 pts
24Thomas County99.1+4.2 pts
26Georgetown County99-0.3 pts
26Socorro County99+0.9 pts
28Apache County98.9-1.1 pts
28Cerro Gordo County98.9+0.3 pts
28Clark County98.9+3.6 pts
31Archuleta County98.8+0.5 pts
32Elko County98.6+11.1 pts
32Muskogee County98.6+1.9 pts
32Polk County98.6+3.8 pts
35Ford County98.4+0.2 pts
35Stutsman County98.4+2.3 pts
35Washington County98.4+2.9 pts
38Alamosa County98.3+0.5 pts
38Aleutians East Borough98.3-1.7 pts
38Delta County98.3-0.8 pts
38Kauai County98.3+2.2 pts
38Keweenaw County98.3+4.2 pts
43Culberson County98.2+1.7 pts
44Yalobusha County98.1-0.7 pts
45Adams County98+15.4 pts
45Prowers County98+1.4 pts
47Big Horn County97.9+10.2 pts
48Caddo County97.8+1.2 pts
48Latah County97.8+10.6 pts
50Lake County97.5+0.8 pts
50Lake County97.5+5.8 pts
50Powell County97.5+5 pts
53Liberty County97.4-0.6 pts
53Routt County97.4-0.7 pts
55McKenzie County97.3+10.8 pts
55Mercer County97.3+15.9 pts
57Cook County97.2+1.1 pts
57Windham County97.2+3.4 pts
59Columbia County97.1+11.3 pts
59Herkimer County97.1-0.4 pts
61Siskiyou County97+5.8 pts
62Hughes County96.9+5.2 pts
63Alexandria city96.7-1 pts
63Meade County96.7+0.3 pts
63Mille Lacs County96.7+0.7 pts
63Sanders County96.7+3.9 pts
67Chaves County96.6+2.7 pts
67Jefferson County96.6+7 pts
67Kitsap County96.6+3.6 pts
67Lubbock County96.6n/a
67Sheridan County96.6+1.8 pts
72Gilmer County96.5-1.2 pts
72Lincoln County96.5-1.7 pts
74Billings County96.4+13.4 pts
74Franklin County96.4+1.7 pts
74Monroe County96.4-0.9 pts
74Taos County96.4-2.2 pts
78Catron County96.3-2.8 pts
79Roosevelt County96.2+3.1 pts
80Merrimack County96.1-1.7 pts
81Prince Edward County96-1.2 pts
82Burke County95.9+16.2 pts
82Hunt County95.9+3 pts
82Oliver County95.9+12.3 pts
82Williams County95.9+11.6 pts
86Franklin County95.8+12.2 pts
86Lauderdale County95.8-2.1 pts
86Warren County95.8+0.5 pts
89Flagler County95.6-3 pts
89Highlands County95.6-1.3 pts
89Potter County95.6+8.3 pts
92Ashland County95.5-0.9 pts
93Fergus County95.4+5.5 pts
93Hamilton County95.4+0.1 pts
93Nye County95.4-2.4 pts
96Butte County95.3+5 pts
97Columbia County95.2+0.7 pts
98Phillips County95.1+8 pts
98St. John the Baptist Parish95.1+1.7 pts
100Burleigh County95+12.5 pts
100Norfolk city95+4 pts
100Park County95+1.3 pts
103Berkeley County94.9-3.7 pts
104Lake County94.8+3.8 pts
104Pointe Coupee Parish94.8+2.2 pts
104St. James Parish94.8+0.6 pts
107Dukes County94.6+4.2 pts
107Jo Daviess County94.6+0.1 pts
107Twin Falls County94.6+8.4 pts
110Jackson County94.5+6.6 pts
110Knox County94.5+2.4 pts
110Okaloosa County94.5-2.5 pts
110Pueblo County94.5+1.5 pts
114Goodhue County94.40 pts
115Dunn County94.3+13.5 pts
115Victoria County94.3+3.8 pts
117Carteret County94.2-0.1 pts
117Kennebec County94.2+3.1 pts
117Middlesex County94.2-1.1 pts
120Lee County94.1-2.9 pts
121Clackamas County94+8.4 pts
121DeKalb County94-1.2 pts
121Smith County94+6.6 pts
121Whitman County94+12 pts
125Luna County93.9-5 pts
125Martin County93.9+22.1 pts
125St. Lucie County93.9-3.5 pts
128Anderson County93.8+1.3 pts
129Manatee County93.7+1.6 pts
129Saratoga County93.7-1.6 pts
131Grant County93.6+13.3 pts
131Mohave County93.6-2.6 pts
133Callaway County93.5+6.6 pts
134Osceola County93.4-3.2 pts
134Story County93.4-1.4 pts
136Baker County93.3-4.5 pts
136Claiborne County93.3-0.6 pts
136Montrose County93.3n/a
139Uinta County93.2+6.6 pts
140Adams County93+2.8 pts
140Canadian County93+7.8 pts
140Macon County93-2.2 pts
143Cherokee County92.9+0.8 pts
143Custer County92.9+3.6 pts
143Forest County92.9+5.1 pts
143Hood County92.9+8.3 pts
143Indian River County92.9-3.2 pts
143Lewis County92.9+6.8 pts
149Elk County92.8-0.6 pts
150Wexford County92.7-1.1 pts
151Adams County92.6+9.9 pts
151Carlton County92.6+6.1 pts
151Klickitat County92.6+3.4 pts
154Beltrami County92.5+2.4 pts
154Boone County92.5+0.4 pts
154Fauquier County92.5-3.7 pts
154Jefferson County92.5-2.3 pts
154McClain County92.5+2.8 pts
159Ascension Parish92.3+2.5 pts
159Barnstable County92.3+1.1 pts
159Knox County92.3-0.2 pts
159Whatcom County92.3+8 pts
163Oswego County92.2-4.7 pts
163Tuscola County92.2-2.2 pts
163Vilas County92.2+1 pts
166Caswell County92.1+32.9 pts
166Newton County92.1+2 pts
168Bremer County92-1.5 pts
168Deschutes County92+11.2 pts
168Leavenworth County92-3.1 pts
171Lyon County91.9+7 pts
171Rockwall County91.9+7 pts
173Dutchess County91.8-2.3 pts
173Greenup County91.8+0.1 pts
173Gregg County91.8+3 pts
173Lawrence County91.8+0.8 pts
173Luzerne County91.8+1.7 pts
173Wythe County91.8-1.1 pts
179Marathon County91.7-2.4 pts
179Tompkins County91.7-2.9 pts
181Abbeville County91.6-6.5 pts
181Moffat County91.6-5.6 pts
181Tucker County91.6-0.2 pts
184Carbon County91.5+2.2 pts
184Cass County91.5+4 pts
184Elmore County91.5-4.2 pts
184Giles County91.5+0.7 pts
184Lycoming County91.5-2.2 pts
184Wayne County91.5-4.9 pts
190Darlington County91.3-2.6 pts
190Greenbrier County91.3-4.9 pts
190Johnston County91.3+2 pts
190Trego County91.3+8.3 pts
194Cowlitz County91.2+6.1 pts
194Parker County91.2+8.7 pts
196Bolivar County91-1.2 pts
197Scott County90.90 pts
198Somerset County90.8-4 pts
198Washington County90.8-1.7 pts
198York County90.8-4.5 pts
201Bell County90.7+6 pts
201Grays Harbor County90.7+2.4 pts
201Morgan County90.7-0.7 pts
201Suffolk city90.7+5.7 pts
205Winona County90.6+0.6 pts
206Charles City County90.5+3.1 pts
206Rockbridge County90.5+3.4 pts
208Skagit County90.4+12.6 pts
209Douglas County90.3+10.3 pts
209Hall County90.3+5.1 pts
211Benton County90.2+4.2 pts
211Clearfield County90.2+3.3 pts
211Essex County90.2+1.7 pts
211Franklin County90.2-7.8 pts
211Honolulu County90.2+12.7 pts
211Natrona County90.2+0.1 pts
217Brookings County90.1+11.8 pts
217Creek County90.1-2.2 pts
219Becker County89.8+8 pts
219Cotton County89.8+3.7 pts
219Hyde County89.8+1.5 pts
219Mayes County89.8-2.5 pts
219St. Martin Parish89.8-1 pts
219Williamson County89.8-2.7 pts
225Aiken County89.7-5.8 pts
225Chattooga County89.7-0.9 pts
225Macoupin County89.7-1.8 pts
225Person County89.7+10.6 pts
229Cascade County89.6+11.5 pts
229Pasco County89.6-4.4 pts
231Belknap County89.5-4.9 pts
231Lake County89.5-5.8 pts
231Niagara County89.5-1.5 pts
234Taney County89.4-0.3 pts
234Trigg County89.4-3 pts
234York County89.4-1.3 pts
237Columbia County89.3-4.1 pts
237Mason County89.3+2 pts
237McLennan County89.3+20.8 pts
237Norfolk County89.3+10.7 pts
237Richland County89.3+7.4 pts
237Simpson County89.3+3.2 pts
243Taylor County89.2+2.6 pts
244Brown County89.1-2.6 pts
244Hancock County89.1+2.8 pts
244Huron County89.1+0.1 pts
244Sheridan County89.1+2 pts
248Chase County89+7.5 pts
248Putnam County89-3.5 pts
248Seminole County89-3.5 pts

Showing the top 250 of 1008. The Excel download has every row.

Other periods

About this ranking

Days with a daily Air Quality Index of 0 to 50 (good) as a percentage of the days of the year with an AQI in a US county. Calculated by Invokely from the day counts in the EPA AirData annual summaries; both counts are stored with each value.

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. 490 counties with data in other periods have no value for 2016 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: good days as a share of days with an AQI, calculated with stored counts. 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: good days as a share of days with an AQI, calculated with stored counts (US counties by share of days with good air quality (US EPA AQI), 2016) [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: good days as a share of days with an AQI, calculated with stored counts, US counties by share of days with good air quality (US EPA AQI), 2016. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/good-air-quality-days-share/us-counties?period=2016. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. US counties by share of days with good air quality (US EPA AQI), 2016. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/good-air-quality-days-share/us-counties?period=2016.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts, US counties by share of days with good air quality (US EPA AQI), 2016 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/good-air-quality-days-share/us-counties?period=2016 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_us_counties_by_share_2016,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts: US counties by share of days with good air quality (US EPA AQI), 2016}},
  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/good-air-quality-days-share/us-counties?period=2016. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. 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: good days as a share of days with an AQI, calculated with stored counts: US counties by share of days with good air quality (US EPA AQI), 2016
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/good-air-quality-days-share/us-counties?period=2016
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/us-counties?period=2016.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. 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 share of days with good air quality (US EPA AQI)?

Carroll County, with 100% in 2016, according to EPA.

Which county has the lowest share of days with good air quality (US EPA AQI)?

Hawaii County, with 0.5% in 2016.

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: good days as a share of days with an AQI, calculated with stored counts. Retrieved 2026-10-12. 490 counties have no value for 2016 and are not ranked.

Share of days with good air quality (US EPA AQI): other rankings

US counties: more rankings