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)

Aleutians East Borough had the highest share of days with good air quality (US EPA AQI) of 1001 counties in 2018, at 100%. Los Angeles County had the lowest, at 1.9%. The median was 75.3%. Source: EPA.

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Highest100Aleutians East Borough
Lowest1.9Los Angeles County
Median75.31001 counties

Map of counties, 2018

%, 2018. 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, 2018

Aleutians East Borough: 100 %Aleutians East Borough100Alexandria city: 100 %Alexandria city100Carroll County: 100 %Carroll County100Catron County: 100 %Catron County100Cerro Gordo County: 100 %Cerro Gordo County100Columbiana County: 100 %Columbiana County100Fremont County: 100 %Fremont County100Georgetown County: 100 %Georgetown County100Hopewell city: 100 %Hopewell city100Kenai Peninsula Borough: 100 %Kenai Peninsula Borough100Los Alamos County: 100 %Los Alamos County100Winchester city: 100 %Winchester city100Meade County: 99.7 %Meade County99.7Putnam County: 99.7 %Putnam County99.7Routt County: 99.7 %Routt County99.7Anderson County: 99.3 %Anderson County99.3Denali Borough: 99.2 %Denali Borough99.2Apache County: 98.9 %Apache County98.9Kauai County: 98.6 %Kauai County98.6Cass County: 98.5 %Cass County98.5Monroe County: 98.4 %Monroe County98.4Prowers County: 98.3 %Prowers County98.3Sherman County: 98.3 %Sherman County98.3Yalobusha County: 97.8 %Yalobusha County97.8Pitkin County: 97.6 %Pitkin County97.6Custer County: 97.5 %Custer County97.5Jackson County: 97.4 %Jackson County97.4Lincoln County: 97.4 %Lincoln County97.4Franklin County: 97.2 %Franklin County97.2Hamilton County: 96.9 %Hamilton County96.9Victoria County: 96.8 %Victoria County96.8Alamosa County: 96.7 %Alamosa County96.7Honolulu County: 96.7 %Honolulu County96.7Washington County: 96.5 %Washington County96.5Lake County: 96.4 %Lake County96.4St. James Parish: 96.2 %St. James Parish96.2Gilmer County: 96.1 %Gilmer County96.1Liberty County: 96.1 %Liberty County96.1Luna County: 96.1 %Luna County96.1Maui County: 96.1 %Maui County96.1Aleutians East Borough: 100 %Aleutians East Borough100Alexandria city: 100 %Alexandria city100Carroll County: 100 %Carroll County100Catron County: 100 %Catron County100Cerro Gordo County: 100 %Cerro Gordo County100Columbiana County: 100 %Columbiana County100Fremont County: 100 %Fremont County100Georgetown County: 100 %Georgetown County100Hopewell city: 100 %Hopewell city100Kenai Peninsula Borough: 100 %Kenai Peninsula Borough100Los Alamos County: 100 %Los Alamos County100Winchester city: 100 %Winchester city100Meade County: 99.7 %Meade County99.7Putnam County: 99.7 %Putnam County99.7Routt County: 99.7 %Routt County99.7Anderson County: 99.3 %Anderson County99.3Denali Borough: 99.2 %Denali Borough99.2Apache County: 98.9 %Apache County98.9Kauai County: 98.6 %Kauai County98.6Cass County: 98.5 %Cass County98.5Monroe County: 98.4 %Monroe County98.4Prowers County: 98.3 %Prowers County98.3Sherman County: 98.3 %Sherman County98.3Yalobusha County: 97.8 %Yalobusha County97.8Pitkin County: 97.6 %Pitkin County97.6Custer County: 97.5 %Custer County97.5Jackson County: 97.4 %Jackson County97.4Lincoln County: 97.4 %Lincoln County97.4Franklin County: 97.2 %Franklin County97.2Hamilton County: 96.9 %Hamilton County96.9Victoria County: 96.8 %Victoria County96.8Alamosa County: 96.7 %Alamosa County96.7Honolulu County: 96.7 %Honolulu County96.7Washington County: 96.5 %Washington County96.5Lake County: 96.4 %Lake County96.4St. James Parish: 96.2 %St. James Parish96.2Gilmer County: 96.1 %Gilmer County96.1Liberty County: 96.1 %Liberty County96.1Luna County: 96.1 %Luna County96.1Maui County: 96.1 %Maui County96.1
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2018 (%)Change on 2017
1Aleutians East Borough1000 pts
1Alexandria city1000 pts
1Carroll County1000 pts
1Catron County100+3.5 pts
1Cerro Gordo County100+0.9 pts
1Columbiana County1000 pts
1Fremont County1000 pts
1Georgetown County100+0.3 pts
1Hopewell city1000 pts
1Kenai Peninsula Borough1000 pts
1Los Alamos County100+0.9 pts
1Winchester city1000 pts
13Meade County99.7+0.8 pts
13Putnam County99.7+0.3 pts
13Routt County99.7+2.3 pts
16Anderson County99.3+3.1 pts
17Denali Borough99.2-0.5 pts
18Apache County98.90 pts
19Kauai County98.6+0.3 pts
20Cass County98.5+6.7 pts
21Monroe County98.4+31.2 pts
22Prowers County98.30 pts
22Sherman County98.30 pts
24Yalobusha County97.8-1.6 pts
25Pitkin County97.6-2.4 pts
26Custer County97.5-1.5 pts
27Jackson County97.4-0.9 pts
27Lincoln County97.4-1.7 pts
29Franklin County97.2-1.7 pts
30Hamilton County96.9+1.6 pts
31Victoria County96.8+3.5 pts
32Alamosa County96.7-2.5 pts
32Honolulu County96.7+3.5 pts
34Washington County96.5-0.5 pts
35Lake County96.4-0.3 pts
36St. James Parish96.2+0.6 pts
37Gilmer County96.1-3.1 pts
37Liberty County96.1-2.5 pts
37Luna County96.1+1.7 pts
37Maui County96.1+4.9 pts
37Mohave County96.1-2.2 pts
42Bethel Census Area96n/a
42Highlands County96+0.5 pts
44Nye County95.9+1.1 pts
45Rowan County95.8+2.6 pts
46Flagler County95.7-0.4 pts
46Greenbrier County95.7+0.7 pts
46Windham County95.7-1.8 pts
49Macon County95.5-1 pts
49Norfolk County95.5+2.9 pts
49Socorro County95.5-2.8 pts
52Knox County95.4+0.1 pts
53Merrimack County95.3-1.4 pts
53Norfolk city95.3+3 pts
55DeKalb County95.1-1 pts
55Fauquier County95.1-2 pts
55Herkimer County95.1-3.6 pts
55Pike County95.1+2.9 pts
55Platte County95.1+5.1 pts
55Polk County95.1-2.3 pts
61St. Lucie County95+0.9 pts
62Wayne County94.9-3.3 pts
63Lycoming County94.8+0.6 pts
64Baker County94.7-0.8 pts
64Clark County94.7-1.7 pts
64Keweenaw County94.7-1.2 pts
67Hyde County94.5-0.2 pts
67Prince Edward County94.5-3.2 pts
67Saratoga County94.5-1.8 pts
70Claiborne County94.4+0.2 pts
70Custer County94.4+4.3 pts
72Kennebec County94.2-0.8 pts
73Berkeley County94.1-0.3 pts
73Huntington County94.1+1.4 pts
73Jackson County94.1+2.9 pts
73Putnam County94.10 pts
77Lincoln County94-1.3 pts
78Carroll County93.9+3.4 pts
78Clark County93.9+6.3 pts
78Jo Daviess County93.9+0.4 pts
81Darlington County93.7+1 pts
81Dutchess County93.7-1.5 pts
83St. John the Baptist Parish93.6+0.5 pts
84Cook County93.5-1.1 pts
85Brown County93.4+4.6 pts
85Choctaw County93.4-1.4 pts
87Clearfield County93.3+1.7 pts
87Jefferson County93.3-1.5 pts
89Luzerne County93.2-3.8 pts
90Adams County93.1+5.8 pts
90Barnstable County93.1+0.4 pts
90Trigg County93.1-1.4 pts
93Lee County93-3.4 pts
94Wexford County92.7-1.7 pts
95Elk County92.6-2.7 pts
95Fayette County92.6+1.3 pts
95Morgan County92.6-3.6 pts
95Morgan County92.6-1.5 pts
95Oswego County92.6-3.5 pts
95Perry County92.6+5.4 pts
95Scioto County92.6-1.6 pts
102Harrison County92.4n/a
102Hughes County92.4-3.9 pts
102Rockwall County92.4+0.2 pts
102San Juan County92.4-7.6 pts
102Somerset County92.4-1.8 pts
107Knox County92.2+2.3 pts
107Tompkins County92.2-3.8 pts
109Charlton County92.1+6.3 pts
109Monroe County92.1-2.1 pts
109Okaloosa County92.1-2.4 pts
112Hancock County92+3.4 pts
112Powell County92+5.3 pts
114Lawrence County91.9+1 pts
114Niagara County91.9-0.1 pts
116Ford County91.8-7.1 pts
116Hendricks County91.8+0.1 pts
116New Hanover County91.8+8.4 pts
119Shelby County91.7+5.7 pts
120Greenup County91.6-5.7 pts
120Prince William County91.6+0.1 pts
120Sumter County91.6+11.9 pts
123Park County91.5+3.9 pts
124Bremer County91.4-1.5 pts
124Chattooga County91.4-5.3 pts
124Coffee County91.4+18.5 pts
124Elmore County91.4-6.4 pts
124Kitsap County91.4+0.8 pts
124Suffolk city91.4-1.7 pts
130Indian River County91.3+0.6 pts
131Archuleta County91.2+4.8 pts
131Lake County91.2-0.6 pts
131St. Martin Parish91.2-0.4 pts
131Thomas County91.2-3.6 pts
131York County91.2+0.1 pts
136Horry County91.1-7.8 pts
136Jefferson County91.1+1.2 pts
138Carteret County91-5.8 pts
138Columbia County91-4.9 pts
138Pointe Coupee Parish91-3.5 pts
138Tucker County91-4.4 pts
138Tuscola County91-3.2 pts
143Caroline County90.9-2.2 pts
143Columbia County90.9+2.5 pts
143Stafford County90.9-5.7 pts
143Sumter County90.9-4.1 pts
147Belknap County90.8+6.1 pts
147Glynn County90.8+3.5 pts
147Muskogee County90.8-7.3 pts
147Washington County90.8-0.9 pts
151Belmont County90.7-0.5 pts
151Hancock County90.7+1.7 pts
151Indiana County90.7+0.2 pts
151Lake County90.7+0.7 pts
151Rockbridge County90.7-1.9 pts
156Dawson County90.6-2 pts
156Posey County90.6+8.1 pts
158Mille Lacs County90.5-5.8 pts
159Gregg County90.4-2.7 pts
159Manatee County90.4-2.8 pts
159Osceola County90.4-4.6 pts
162Martin County90.3-4.4 pts
163Brazoria County90.1+4.4 pts
163Carlton County90.1-1.4 pts
163Hunt County90.1-3.9 pts
163Macoupin County90.1+0.8 pts
163Noble County90.1+2.8 pts
168Ashland County90-8.6 pts
169Leavenworth County89.8-4.4 pts
169Monmouth County89.8-5.2 pts
171Boone County89.7-3.6 pts
171Dukes County89.7-3.9 pts
171Mason County89.7+1.1 pts
171Shelby County89.7-3.2 pts
175Charles City County89.6+1.7 pts
175Hillsborough County89.6-2.5 pts
175Latah County89.6+1.3 pts
175Lenoir County89.6-2.2 pts
175Newton County89.6-3 pts
180Potter County89.5-2.7 pts
181Avery County89.4-1.4 pts
181Big Horn County89.4-5.1 pts
183Ascension Parish89.3-2.7 pts
184Goodhue County89.2-5.1 pts
185Ouachita Parish89+3.7 pts
185Skagit County890 pts
185Smith County89-3.3 pts
188Delta County88.9-10.2 pts
188Parker County88.9-1.9 pts
190Boone County88.8-0.6 pts
190Door County88.8-1.5 pts
190Grays Harbor County88.8+3 pts
190Pasco County88.8-0.9 pts
190Rockingham County88.80 pts
190Warrick County88.8+2.3 pts
196Giles County88.7-4.7 pts
197Roosevelt County88.6-5.8 pts
198Douglas County88.4+1.9 pts
198Marathon County88.4-5.7 pts
198Person County88.4-2.5 pts
198Sheridan County88.4-7.2 pts
198Whatcom County88.4+2.2 pts
203Carter County88.3-3.3 pts
204Columbia County88.2-0.8 pts
204Le Flore County88.2n/a
204Rock County88.2+1.4 pts
204Washington County88.2-1.2 pts
208Creek County88.1-0.6 pts
208Oldham County88.1+0.3 pts
210Huron County88-4.9 pts
210Schoolcraft County88-2.5 pts
212Livingston County87.9-2.4 pts
212Wayne County87.9-5.9 pts
214Beltrami County87.8+0.8 pts
214Hanover County87.8-2.5 pts
214Pueblo County87.8-2.6 pts
214Ward County87.8-1.4 pts
218Bell County87.7+4.7 pts
219Bell County87.5-0.3 pts
220Mayes County87.4-4.2 pts
220Morris County87.4-0.2 pts
220Taos County87.4-5.8 pts
223Clinton County87.3-1.4 pts
223Effingham County87.3+2.9 pts
223Fond du Lac County87.3-4.2 pts
223Hood County87.3-3.5 pts
223Jessamine County87.3-4.9 pts
223Wythe County87.3-7 pts
229Benzie County87.2-1.3 pts
229Simpson County87.2-5.6 pts
231Alachua County87.1+11.9 pts
231Knox County87.1-3.9 pts
233Lauderdale County87-11 pts
233Monroe County87+17.8 pts
233Wabash County87-4 pts
236Delaware County86.9-6.2 pts
236Harrison County86.9+2.1 pts
236Wood County86.9-1.7 pts
239Essex County86.8+2.4 pts
239Pickens County86.8-4.3 pts
241Missaukee County86.6+1.4 pts
242Adams County86.5-6.9 pts
242Benton County86.5+4.1 pts
242Bucks County86.5+0.2 pts
242Chesterfield County86.5+1.6 pts
242Williamson County86.5-5.1 pts
247Chaves County86.4-6.9 pts
247Lake County86.4-1.9 pts
249DeKalb County86.3+1.3 pts
250Blaine County86.2-3.3 pts

Showing the top 250 of 1001. 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. 497 counties with data in other periods have no value for 2018 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), 2018) [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), 2018. 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=2018. 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), 2018. 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=2018.

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), 2018 [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=2018 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_us_counties_by_share_2018,
  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), 2018}},
  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=2018. 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), 2018
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=2018
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/us-counties?period=2018.
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)?

Aleutians East Borough, with 100% in 2018, according to EPA.

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

Los Angeles County, with 1.9% in 2018.

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. 497 counties have no value for 2018 and are not ranked.

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

US counties: more rankings