In late June 1995, Chicago experienced an intense heat wave that combined prolonged high temperatures, extreme humidity, and stagnant air. Beginning in mid-June and peaking around June 30, the region endured several consecutive days with daytime highs in the 90s and nighttime lows that offered little relief. The heat wave disproportionately affected the elderly, people with chronic illnesses, those living alone, and residents of low-income neighborhoods where access to air conditioning and cooling centers was limited. Meteorological conditions A strong high-pressure system parked over the Midwest suppressed cloud formation and ventilation, trapping heat near the surface. Heat indices—measures that combine temperature and humidity to estimate apparent temperature—reached dangerous levels. Nighttime temperatures remained elevated, preventing physiological recovery from daytime heat. Urban heat island effects in Chicago amplified surface and near-surface temperatures within densely built neighborhoods. Human toll and demographics Estimates of excess mortality from the event vary by source and method, but contemporaneous public health analyses and later studies attributed roughly 700 to 750 deaths in Chicago and surrounding Cook County to the heat wave. Many victims were older adults living alone in apartment buildings without working air conditioning or with limited mobility. Black and low-income neighborhoods experienced particularly high mortality rates, reflecting disparities in housing, access to cooling, social isolation, and underlying health conditions. Public health response and challenges City and county agencies, social service organizations, and faith-based groups mobilized to open cooling centers, check on vulnerable residents, and distribute water. However, communication gaps, limited outreach to isolated individuals, and insufficient resources constrained the response. Coroners and public health officials initially struggled to classify heat-related deaths consistently, and some fatalities were identified only after excess-mortality analyses compared observed deaths to expected baselines. Long-term impact and lessons The 1995 heat wave prompted changes in urban heat and public-health planning. Chicago and other cities expanded heat emergency protocols, improved notification systems, increased the availability of cooling centers, and invested in outreach programs targeting vulnerable populations. The event also spurred research into heat-related mortality, urban heat island mitigation (such as increased tree canopy and reflective surfaces), and the role of social isolation in extreme-weather vulnerability. Historical context and continuing relevance At the time, the Chicago event stood out as one of the deadliest heat waves in recent U.S. history. Subsequent heat-related disasters elsewhere have underscored that extreme heat remains a major and growing public-health threat, particularly as climate change increases the frequency, intensity, and duration of heat waves. Researchers and policymakers continue to cite the 1995 Chicago heat wave when designing heat-health interventions and assessing the need for targeted support to at-risk communities. Sources and caveats Numbers and attributions come from contemporaneous public-health reports, coroner and medical-examiner data, and later epidemiological studies that analyzed excess mortality during and after the event. Estimates of deaths vary by methodology and geographic scope; some reports focus on city limits while others include surrounding Cook County. Because classification of heat-related mortality can be complex, figures are best understood as approximate and dependent on the analytical approach.