weatherbycounty

Counties with the Most Extreme Heat Days

Published May 2, 2026

Extreme heat — defined as days where the temperature exceeds 90°F — is one of the most challenging aspects of American climate. For residents of the hottest counties, extreme heat is not an occasional inconvenience but a persistent feature of daily life that shapes everything from energy bills to outdoor activity patterns.

We analyzed NOAA 30-year climate normals to find the counties that endure the most extreme heat days annually. The results reveal a clear geographic pattern concentrated in the desert Southwest, the Central Valley of California, and the Deep South.

The 25 Counties with the Most Extreme Heat Days

Starr County, TX tops the list with an average of 190.75 days per year above 90°F.

RankCountyStateHeat Days/YearAvg July Temp (°F)Avg Annual Temp (°F)
1Starr CountyTX190.7588.2575.5
2Yuma CountyAZ180.3428571428571693.1714285714285874.05714285714286
3Imperial CountyCA180.0692.2273.67999999999999
4La Paz CountyAZ177.9599999999999893.772.4
5Webb CountyTX174.4587.273.4
6Zapata CountyTX171.887.474.4
7Hidalgo CountyTX171.2777777777777486.4555555555555674.84444444444443
8Maricopa CountyAZ167.2200000000000391.6750000000000171.775
9Brooks CountyTX160.385.472.2
10Jim Hogg CountyTX157.686.873.9
11Pinal CountyAZ157.318181818181889.4818181818181870.10909090909091
12La Salle CountyTX156.9586.372
13Duval CountyTX154.985.4571.94999999999999
14Kenedy CountyTX154.6000000000000284.2572.65
15Zavala CountyTX153.686.472.7
16Dimmit CountyTX152.986.170.6
17Maverick CountyTX151.285.670.2
18McMullen CountyTX148.7333333333333285.8333333333333371.46666666666665
19Kleberg CountyTX147.685.773.3
20Brewster CountyTX144.207692307692383.467.93846153846152
21Jim Wells CountyTX143.5333333333333385.3333333333333372.63333333333333
22Inyo CountyCA141.6400000000000189.4600000000000166.64
23Atascosa CountyTX140.8666666666666585.3999999999999971
24Frio CountyTX139.985.471
25Riverside CountyCA139.8277777777777885.9666666666666569.54444444444444

Important

Extreme heat is the leading weather-related cause of death in the United States. If you live in or are considering a move to a high heat-day county, ensure your home has reliable air conditioning and understand local heat emergency protocols.

Methodology

Extreme heat days are defined as days where the maximum temperature exceeds 90°F, based on NOAA NCEI 1991-2020 climate normals. Data represents 30-year averages, not individual year records. Approximately 89% of US counties have sufficient weather station coverage for reliable climate normals.

Data source: NOAA National Centers for Environmental Information (NCEI), U.S. Climate Normals 1991-2020. All figures represent 30-year averages and may differ from individual-year observations. Station-level data is aggregated to county level using spatial averaging.

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