PHOENIX, AZ — Maricopa County has confirmed 40 heat-related deaths so far this year, with hundreds more still under investigation as another stretch of extreme heat grips the Valley.
County health officials said 388 additional deaths remain under review to determine whether heat played a role.
Among the confirmed deaths, 77% of victims were found outdoors, 65% involved substance use, and 33% involved people experiencing homelessness.
The latest figures come as Phoenix and much of the Valley remain under an Extreme Heat Warning through 8 p.m. Sunday. The National Weather Service is forecasting afternoon highs between 109 and 117 degrees, with Major to Extreme Heat Risk across the region.
Preliminary county data shows 430 heat-related deaths in 2025, down from 608 in 2024 and 645 in 2023. Even with the recent dip, the numbers remain far above the totals seen a decade ago, when Maricopa County recorded 84 heat-related deaths in 2015.
Annual heat-related deaths in Maricopa County have climbed sharply over the past 10 years:
Health officials say the danger is not limited to the hottest days of the year. Nearly half of the heat-related deaths in 2025 occurred on days when the official heat risk level was only moderate.
Other patterns in the data were also notable. About 47% of victims had cardiovascular disease listed as a contributing factor, nearly 49% were experiencing homelessness, nearly three-quarters were male, and about 60% were age 50 or older.
Phoenix accounted for the largest share of heat-related deaths in 2025 with 233, followed by Mesa with 39 and Tempe with 18.
Heat Relief Network sites, including cooling centers, respite centers and hydration stations, are open across nearly every city in the Valley through Sept. 30 for residents who need access to cool indoor spaces. Hours vary by location, and officials recommend checking online before going.
Residents can find nearby locations through the Heat Relief Regional Network or by calling 2-1-1.
Officials are also urging residents to know their personal risk factors, including age, health conditions, certain medications, unstable housing and substance use, which can increase vulnerability to heat even on days without an official warning.
Recognizing early signs of heat illness is critical, health officials say. Dizziness, nausea, headache, heavy sweating and weakness can signal that the body is overheating.
If symptoms worsen, officials recommend moving to a cooler location, hydrating and seeking medical care. Heat stroke is a medical emergency, and anyone showing signs of it should be moved to a cool, shaded area immediately while someone calls 911.
For people working or spending long periods outdoors, the Occupational Safety and Health Administration recommends frequent breaks in shaded or air-conditioned areas, shifting strenuous activity to early morning or evening hours when possible, wearing lightweight loose-fitting clothing and drinking water throughout the day.
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