At least 14 people have died in Cook County this summer from heat-related causes, with July marking the area’s deadliest month for heat-related deaths in more than a decade, according to data from the medical examiner’s office. Successive heat waves in late June and early-to-mid-July this year pushed the heat index, a combination of temperature and humidity, above 100 degrees for several days.
The majority of the people who died in Cook County had underlying health issues that were complicated by the extreme heat, according to the medical examiner’s office, including cardiovascular disease, hypertension and obesity. Periods of extreme heat can add stress to these conditions, triggering heart attacks, strokes and heart failure. However, these interactions can complicate an accurate count of heat-related mortalities, as preexisting conditions can obscure the role extreme temperatures had in someone’s death.
Heat deaths are “almost certainly undercounted,” said Abel Kho, an internist and professor of medicine and preventive medicine at Northwestern University’s Feinberg School of Medicine. “It has a lot to do with the way we document in our death records, and we’ve known that for a long time, too.”
Health professionals say science needs to draw clearer lines between heat and certain health outcomes, including death, to better prepare public health responses to longer, hotter stretches of summer weather that area residents are going to experience under climate change.
“They’re going by the death certificates, and instead of … hundreds and hundreds of people who died this summer in Chicago from excess heat, there were — what’s the number? Fourteen. It’s probably 20, 30, 40 times that,” said Howard Ehrman, a former Chicago assistant health commissioner and a retired assistant professor of family medicine and public health at the University of Illinois Chicago.
After Chicago’s 1995 heat wave, which killed more than 700 people, the county saw 10 heat-related deaths in 1999 and 23 in 2012, the Tribune reported. Before this July, the highest monthly heat-related death toll since 2015 in the county came in July 2019, when five people died, according to the medical examiner. According to the Chicago Department of Public Health, the city had an average of three heat-related deaths per year from 2020 to 2024.
More people are killed and hospitalized during heat waves than any other extreme weather event, experts say. As human activities like fossil fuel burning release heat-trapping gases into the atmosphere and increase global temperatures, Chicago’s average summer temperatures have increased by 1.9 degrees since 1970 as Midwest summers become more humid. Average lows on summer nights have increased by at least 2.5 degrees in that same time, offering the human body little to no relief.
Ponni Arunkumar, the Cook County chief medical examiner, said the office does not get called to investigate all suspected heat-related deaths, since a person’s treating physician often signs the death certificate.
“If the physician(s) … know that there is heat involved, then they know to call our office,” she said. But sometimes a case might not be classified as a heat death and reported as such, especially if the circumstances of death are unknown, “so there is that underreporting” as cases fall through the cracks.
A Northwestern study published in the scientific journal Science Advances in August found that heat was linked to a much wider range of health problems in Chicago-area emergency departments and urgent care clinics over the past 13 years than just dehydration and heat stroke, conditions more commonly associated with warmer temperatures.
“While yes, (heat) does lead to premature mortality sometimes, there’s a whole bunch of things that happen on the way to dying that are also bad,” said Daniel Horton, one of the study’s authors, a Northwestern associate professor and lead of the Defusing Disasters Working Group at the Buffett Institute for Global Affairs.
Specifically, the study identified 33 diagnoses linked to exposure to extreme heat, including skin rashes, leg swelling, kidney disease, multiple sclerosis and mental health disorders. So, during periods of hotter temperatures in the Chicago area, emergency rooms see increased visits for a lot of different symptoms, diseases and injuries — including conditions that are not often associated with heat in medical records, which historically has made the impact of heat on health outcomes difficult to track.
Some of the findings were expected, but others were more surprising, including an increase in traffic accidents, firearm-related injuries and assault.
“Experiencing heat is a stressful thing,” Horton said. “There’s been all sorts of research that has indicated that aggression goes up.”
Kho, the senior author of the study, said a deeper understanding of the more subtle effects of heat on different health outcomes can inform better preparedness for extreme heat events.
“If we were to mitigate these heat events or these heat stressors, … could we bend the curve and actually reduce mortality in total?” he said.
Extreme heat exacerbates underlying health conditions that tend to be more prevalent in communities of color where rates of chronic respiratory and cardiovascular disease are higher than the Chicago average, according to city data. More than half of the people who died from heat complications across the county this summer were people of color: Five were Black and four were Latino.
Eleven of Cook County’s heat deaths occurred in Chicago, specifically in neighborhoods on the South and West sides: East Garfield Park, Near West Side, McKinley Park, New City, Chicago Lawn, Englewood, Greater Grand Crossing, Chatham, Avalon Park and East Side.
“People’s health and their propensity toward illness is driven so much by these non-medical factors, … the social determinants that people talk about. It’s where you grow up and where you live,” Kho said. “We know that there’s a big life expectancy gap in Chicago, driven by less opportunity, and that leads to greater incidence of chronic disease.”
The most recent victim of heat was Billy J. Humphrey, 78, who died Sept. 2 of organic cardiovascular disease. The medical examiner listed heat stress as a secondary cause. The temperature high recorded at O’Hare International Airport that day was 96 degrees, and the low was 78 — both 16 degrees above normal, according to National Weather Service data. The local office said Sept. 1-4, 2026, was the hottest four-day start to any September on record for Chicago.
John Aubrey Vaughan, 69, died July 2 in Chatham of hypertensive heart disease. Chronic alcoholism and heat stress were listed as contributing factors. His autopsy results had been pending until Aug. 14, which is why the Tribune hadn’t previously identified him as one of the people who died during the Independence Day weekend heat wave.
Most heat deaths within city limits this summer happened only blocks from a green space like a public park, or at least from one of Chicago’s so-called cooling centers: A library, a police station, a senior center or a park district fieldhouse or water spray feature. This reality highlights advocates’ concerns that the city does not adequately advertise these resources or that they are not as accessible as they could be, especially overnight, on weekends or during holidays, for people who are homeless or who don’t have adequate cooling options at home.
As Chicago heats up, advocates and experts slam city for not addressing ‘inadequate’ cooling network
Horton, who helped develop the Chicago Heat Vulnerability Index — a data tool that identifies the communities in the city that face the highest risk during extreme heat — said vulnerability is not a mathematical formula. Rather, a lot of factors and interpretations go into assessing said risk.
“Certainly, someone’s ability to access a cooling center will determine their vulnerability. Someone’s ability to turn on their air conditioning or have air conditioning to begin with, that can influence their vulnerability,” he said. “And you know, this social cohesion or the social network is another big piece because we know that people that are isolated are often impacted by heat, and so if you don’t have the community that’s kind of looking out for you, that can be a real vulnerability.”
Kho emphasized that some of the most vulnerable to environmental stressors like heat are those less socially connected.
“There’s a real good reason why people who are homeless or older individuals are really at risk. And it’s not just because they may have other comorbid conditions,” he said. “It may be because they’re, again, very much disconnected, and even when resources are right there, for all kinds of reasons … they may simply be unable to (take) that series of steps themselves.”
Otto George Kendzior, 63, of Dolton, died Aug. 4 on Chicago’s Near West Side, in the heart of the Illinois Medical District. On July 14, 65-year-old Joseph W. Huff died in the village of Oak Lawn. Both deaths were ruled natural, with the primary cause being organic cardiovascular disease and the secondary cause being heat stress.
A second death also was tied to the heat wave that started July 13, during which highs stayed above 90 for six consecutive days, reaching 96 degrees, and lows barely dropped below 70.
On July 17, 33-year-old Jesus C. Rodriguez died of hyperthermia — having an abnormally high core body temperature — and drug toxicity in the East Side community area, on the city’s Far South Side. His autopsy results, like Vaughan’s, also were only available a month later.
As a cause of death, hyperthermia often is diagnosed by excluding every other possibility, since body temperature at the time of death is not always available or knowable. Extensive testing, alongside the careful study of the circumstances surrounding a death, can thus delay the autopsy results. Arunkumar said the medical examiner’s office thoroughly investigates the cases it is called on to determine whether heat was a main or contributing factor.
“In some instances, it takes some time to get all the toxicology testing done, and it takes some time to get these results, look at all of them with the circumstances that they were found in, to say if the death is due to or in part related to heat,” Arunkumar said. “So, it is normal to have some cases where we need that additional testing before we say the death is due to heat.”
Stimulant drugs like cocaine or amphetamine increase the body temperature, which can make someone more vulnerable to heat, she said, and determining their presence often requires additional tests. And, if someone is under the influence of alcohol or drugs, that might also impair that person’s ability to take care of themselves.
Heat also can cause health problems and lead to deaths several days, weeks or even months after a heat wave ends. For instance, the first heat wave this summer lasted June 30 through July 2, when highs reached the mid-90s and indices were over 100, but some people affected by that heat died later in July.
Robert Feldon, 77, of Westchester, died July 10 after complications from a fall more than a week earlier. The medical examiner ruled his death accidental, with several secondary causes listed, including heat stress, tachycardia and osteoporosis.
Stephanie Rodriguez, 45, died July 9 in the Greater Grand Crossing neighborhood from complications of heat stroke 10 days earlier, according to the medical examiner’s office. Schizophrenia was listed as a secondary cause of death. Kho said mental health disorders cannot only be exacerbated during periods of extreme heat, but also make it harder for a person to know where or how to seek help.
Improving medical record-keeping — especially among populations without regular access to healthcare — can allow for a clearer understanding of the long-term effects of heat on the human body, Horton said, “and that’s ultimately our goal: To try to understand all the things, all the negative public health outcomes, and how they’re linked together.”
“This type of work, I think, can allow us to start tying together a story, a clearer story,” Kho said. “From how did a person die, you can track back through electronic records, and you may be able to find a much more clear relationship with heat, even if heat wasn’t physically documented somewhere. I think there’s a real opportunity for us to try to tie together different types of data … the full clinical record, not just what happened on the death record.”
On July 3, Barbara Whigham and Mike Rodríguez also died of heart disease complicated by heat stress. Whigham, 71, who died in Englewood, had asthma and obesity. Rodríguez, 57, who died in McKinley Park, had diabetes, according to the medical examiner’s office.
After autopsy results were pending for more than a month, the Cook County medical examiner confirmed Claramon Elizabeth Little, 94, died of heat stroke in the Greater Grand Crossing neighborhood on July 2. Heat stroke, like hyperthermia, also is determined through an often lengthy diagnostic process of exclusion.
Victor Ferguson, a 48-year-old West Side resident, died July 2 of heat stroke, with alcohol poisoning listed as a secondary cause.
In Chicago Lawn, two men in their 40s died over the Independence Day weekend blocks from each other. David González, 44, died of heat stroke July 4. The medical examiner’s office listed diabetes and obesity as contributing factors to his death. David Pedro Sopys, 46, had died three days earlier from hyperthermia, with drug intoxication being a contributing factor.
A day earlier, 69-year-old Daniel Machnikowski died at his Evanston home of heart disease, with heat stress listed as a contributing factor. He was the first recorded person to die from warm temperatures in the county this summer.
Chicago Tribune’s Lila Hempel-Edgers, Evgenia Anastasakos and Tess Kenny contributed.
