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Extreme Heat Risk by County
Which counties face the highest risk from heat waves.
2 counties share the top score of 100 out of 100 on FEMA's National Risk Index: Philadelphia County, Pennsylvania, Maricopa County, Arizona.
Open the live map →☀️Highest-scoring counties
| County | Fema heat risk score (0-100) |
|---|---|
| Philadelphia County, Pennsylvania | 100 |
| Maricopa County, Arizona | 100 |
| St. Louis County, Missouri | 99.9 |
| Dallas County, Texas | 99.9 |
| Clark County, Nevada | 99.9 |
| Pima County, Arizona | 99.8 |
| St. Louis city, Missouri | 99.8 |
| Cook County, Illinois | 99.8 |
| Kings County, New York | 99.7 |
| Harris County, Texas | 99.7 |
🌡️States with the most top-5% counties
🔎About this data
FEMA's long-run heat-wave risk score, compared with other U.S. counties.
Source: FEMA National Risk Index v1.20 (December 2025), county scores
Coverage: Nationwide (counties)
Single source: FEMA's recorded tornado events for Oklahoma, Kansas and Alabama compared with NOAA storm records (moderate agreement, as expected for a long-run model). FEMA's scores are modelled estimates, so this layer is labelled single source.
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💬Questions and answers
Which county has the highest extreme heat risk?
2 counties share the top score of 100 out of 100 on FEMA's National Risk Index: Philadelphia County, Pennsylvania, Maricopa County, Arizona.
Which state has the most high-risk counties?
California has the most counties in the top 5% (20 of the 158 counties scoring 95 or more).
What does the score mean?
FEMA's National Risk Index scores each county from 0 to 100 compared with all other U.S. counties: a score of 95 means the county's expected long-run losses are higher than 95% of counties. It is a model of risk over many years, not a forecast.
Where does this data come from?
FEMA National Risk Index v1.20 (December 2025), county scores. Coverage: Nationwide (counties).
Is the map free to use?
Yes. Map the Block is free, with no ads or paywall. You may quote figures with credit to Map the Block (maptheblock.com); for bulk or commercial use there is a Data API.
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Numbers computed from the live map data on October 18, 2026. Free to quote with credit to “Map the Block (maptheblock.com)”; see reuse terms.