Data / Rankings / Share of days with good air quality (US EPA AQI) / Counties in Missouri

Counties in Missouri by share of days with good air quality (US EPA AQI)

Monroe County had the highest share of days with good air quality (US EPA AQI) of 21 counties in 2021, at 98.4%. St. Louis city had the lowest, at 31.2%. The median was 82.8%. Source: EPA.

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Highest98.4Monroe County
Lowest31.2St. Louis city
Median82.821 counties

Map of counties, 2021

Andrew County: 91.8 %Boone County: 95.1 %Buchanan County: 64.4 %Callaway County: 93.5 %Cass County: 73.2 %Cedar County: 69.1 %Clay County: 77.1 %Clinton County: 90.2 %Greene County: 82.2 %Jackson County: 36.2 %Jasper County: 82.8 %Jefferson County: 66.8 %Lincoln County: 92.2 %Monroe County: 98.4 %Perry County: 87.3 %St. Charles County: 85.3 %Ste. Genevieve County: 92.7 %St. Louis County: 68.8 %Stoddard County: 77.1 %Taney County: 86.4 %St. Louis city: 31.2 %
  • Under 69
  • 69 to 77
  • 77 to 86
  • 86 to 92
  • 92 and over
  • No data
%, 2021. Hatched areas have no value for this period. Source: Invokely calculation with data from EPA. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2021

Monroe County: 98.4 %Monroe County98.4Boone County: 95.1 %Boone County95.1Callaway County: 93.5 %Callaway County93.5Ste. Genevieve County: 92.7 %Ste. Genevieve County92.7Lincoln County: 92.2 %Lincoln County92.2Andrew County: 91.8 %Andrew County91.8Clinton County: 90.2 %Clinton County90.2Perry County: 87.3 %Perry County87.3Taney County: 86.4 %Taney County86.4St. Charles County: 85.3 %St. Charles County85.3Jasper County: 82.8 %Jasper County82.8Greene County: 82.2 %Greene County82.2Clay County: 77.1 %Clay County77.1Stoddard County: 77.1 %Stoddard County77.1Cass County: 73.2 %Cass County73.2Cedar County: 69.1 %Cedar County69.1St. Louis County: 68.8 %St. Louis County68.8Jefferson County: 66.8 %Jefferson County66.8Buchanan County: 64.4 %Buchanan County64.4Jackson County: 36.2 %Jackson County36.2St. Louis city: 31.2 %St. Louis city31.2Monroe County: 98.4 %Monroe County98.4Boone County: 95.1 %Boone County95.1Callaway County: 93.5 %Callaway County93.5Ste. Genevieve County: 92.7 %Ste. Genevieve County92.7Lincoln County: 92.2 %Lincoln County92.2Andrew County: 91.8 %Andrew County91.8Clinton County: 90.2 %Clinton County90.2Perry County: 87.3 %Perry County87.3Taney County: 86.4 %Taney County86.4St. Charles County: 85.3 %St. Charles County85.3Jasper County: 82.8 %Jasper County82.8Greene County: 82.2 %Greene County82.2Clay County: 77.1 %Clay County77.1Stoddard County: 77.1 %Stoddard County77.1Cass County: 73.2 %Cass County73.2Cedar County: 69.1 %Cedar County69.1St. Louis County: 68.8 %St. Louis County68.8Jefferson County: 66.8 %Jefferson County66.8Buchanan County: 64.4 %Buchanan County64.4Jackson County: 36.2 %Jackson County36.2St. Louis city: 31.2 %St. Louis city31.2
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2021 (%)Change on 2020
1Monroe County98.40 pts
2Boone County95.1-1.2 pts
3Callaway County93.5-2 pts
4Ste. Genevieve County92.7-0.8 pts
5Lincoln County92.2-0.9 pts
6Andrew County91.80 pts
7Clinton County90.2-2 pts
8Perry County87.3-7 pts
9Taney County86.4-6.2 pts
10St. Charles County85.3-2.9 pts
11Jasper County82.8-4.6 pts
12Greene County82.2+8.6 pts
13Clay County77.1-1.7 pts
13Stoddard County77.1-8.6 pts
15Cass County73.2-9.7 pts
16Cedar County69.1-9.6 pts
17St. Louis County68.8+1.6 pts
18Jefferson County66.8-1.7 pts
19Buchanan County64.4-3.5 pts
20Jackson County36.2-11.6 pts
21St. Louis city31.2-6.2 pts

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. 13 counties with data in other periods have no value for 2021 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 (Counties in Missouri by share of days with good air quality (US EPA AQI), 2021) [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, Counties in Missouri by share of days with good air quality (US EPA AQI), 2021. 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/missouri-counties?period=2021. 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. Counties in Missouri by share of days with good air quality (US EPA AQI), 2021. 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/missouri-counties?period=2021.

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, Counties in Missouri by share of days with good air quality (US EPA AQI), 2021 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/good-air-quality-days-share/missouri-counties?period=2021 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_missouri_by_2021,
  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: Counties in Missouri by share of days with good air quality (US EPA AQI), 2021}},
  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/missouri-counties?period=2021. 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: Counties in Missouri by share of days with good air quality (US EPA AQI), 2021
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/missouri-counties?period=2021
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/missouri-counties?period=2021.
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)?

Monroe County, with 98.4% in 2021, according to EPA.

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

St. Louis city, with 31.2% in 2021.

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. 13 counties have no value for 2021 and are not ranked.

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

Counties in Missouri: more rankings