Counties in Texas by highest daily Air Quality Index (US EPA)

Harris County had the highest highest daily Air Quality Index (US EPA) of 41 counties in 2019, at 202. Potter County had the lowest, at 65. The median was 107. Source: the U.S. Environmental Protection Agency.

Highest202Harris County

Lowest65Potter County

Median10741 counties

Map of counties, 2019

Under 91
91 to 100
100 to 110
110 to 130
130 to 140
140 and over
No data

index, 2019. Hatched areas have no value for this period. Source: EPA, EPA AirData annual AQI by county: highest daily AQI. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2019

index. Source: EPA, EPA AirData annual AQI by county: highest daily AQI. Retrieved 2026-10-12.

Full ranking

Rank	Counties	2019 index	Change on 2018
1	Harris County	202	-2
2	Bexar County	175	+9
3	Brazoria County	161	-5
4	El Paso County	159	-5
5	Collin County	156	+6
6	Jefferson County	150	-4
7	Tarrant County	147	-19
8	Dallas County	143	-18
8	Johnson County	143	-13
8	Montgomery County	143	-13
11	Galveston County	136	-66
12	Denton County	133	-18
12	Hood County	133	0
12	Smith County	133	+21
15	Travis County	115	0
16	Gregg County	112	+15
16	Randall County	112	0
18	Bowie County	109	+3
18	Webb County	109	+2
20	Culberson County	108	+27
21	Nueces County	107	+8
22	Hidalgo County	106	-9
23	Bell County	105	-31
23	Rockwall County	105	-31
25	Maverick County	104	+4
26	Lubbock County	103	-31
27	Navarro County	100	-17
27	Orange County	100	-22
27	Parker County	100	-64
30	Ellis County	97	-23
30	Hunt County	97	-57
32	Brewster County	93	-4
32	Kaufman County	93	-29
34	Cameron County	91	-8
35	Harrison County	90	-21
36	Kleberg County	89	-75
37	McLennan County	87	-11
37	Victoria County	87	-25
39	Ector County	82	-10
40	Polk County	74	-23
41	Potter County	65	-69

Other periods

About this ranking

Highest daily Air Quality Index (AQI) value recorded in a US county during the year, from the EPA AirData annual summaries. Values above 500 are beyond the AQI scale and are published as EPA computes them.

A single day decides the value, so one wildfire or dust event can set it. Dust from the dry Owens Lake bed puts Inyo and Mono counties in California in the thousands. 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. 22 counties with data in other periods have no value for 2019 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: highest daily AQI. 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: highest daily AQI (Counties in Texas by highest daily Air Quality Index (US EPA), 2019) [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: highest daily AQI, Counties in Texas by highest daily Air Quality Index (US EPA), 2019. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/highest-daily-air-quality-index/texas-counties?period=2019. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: highest daily AQI. Counties in Texas by highest daily Air Quality Index (US EPA), 2019. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/highest-daily-air-quality-index/texas-counties?period=2019.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: highest daily AQI, Counties in Texas by highest daily Air Quality Index (US EPA), 2019 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/highest-daily-air-quality-index/texas-counties?period=2019 (Accessed: 12 October 2026).

BibTeX

@misc{environmental_counties_in_texas_by_2019,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: highest daily AQI: Counties in Texas by highest daily Air Quality Index (US EPA), 2019}},
  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/highest-daily-air-quality-index/texas-counties?period=2019. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: highest daily AQI. 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: highest daily AQI: Counties in Texas by highest daily Air Quality Index (US EPA), 2019
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/highest-daily-air-quality-index/texas-counties?period=2019
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/highest-daily-air-quality-index/texas-counties?period=2019.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: highest daily AQI. 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 highest daily Air Quality Index (US EPA)?

Harris County, with 202 in 2019, according to the U.S. Environmental Protection Agency.

Which county has the lowest highest daily Air Quality Index (US EPA)?

Potter County, with 65 in 2019.

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: highest daily AQI. Retrieved 2026-10-12. 22 counties have no value for 2019 and are not ranked.