Due to consistent temperature rise, damages from heatwaves are steadily increasing as time passes. Consequently, national attention towards heatwaves has heightened, leading to a significant rise in preliminary research aimed at analyzing this phenomenon. However, previous research on heatwaves has been limited to topics within climatology, impact variables, risk assessment, and related subjects in meteorology and vulnerability. In this study, the concept and methodology of social autopsy were introduced to analyze the causes of heatwave damage from a sociological perspective through social and environmental analysis. Firstly, the heatwave damage indicator selected for analysis was the number of heat-related illness cases, and the region chosen for the application of social autopsy was Jeju Island, where heat-related illnesses are most pronounced in the country. For the selected area, a control group was identified by contrasting areas with similar environmental conditions but significant differences in the prevalence of heat-related illnesses. Social and environmental factors were then analyzed based on personal social relationships, socioecological structures, and geographical characteristics to analyze heat-related illnesses in different regions. In a quantitative study analyzing the socio-ecological structure using social capital assessments, the results showed that in areas with a high incidence of heat-related illnesses (Hwabuk-dong, Gujo-eup), the probability of experiencing heat-related illnesses increased by 3.2 times when personal organizational trust and residential relationships increased. In contrast, the probabilities decreased by 91.5% and 95.1%, respectively, with an increase in mobile communication and participation in elections. Next, for the analysis of individual temperament and living environment, qualitative research through in-depth interviews was conducted with direct victims who sought medical attention for heat-related illnesses. The results revealed that all subjects exhibited high responsibility, diligence, and proactiveness, with a low level of awareness of the risk of heat-related illnesses. Additionally, growing up in environments with economic difficulties during childhood and youth was associated with a sense of responsibility and diligence, demonstrating a connection to the burden of taking responsibility for family and home, and continuing to work without stopping despite exposure to risks (heat-related illnesses). Finally, an analysis of the geographical characteristics of the region revealed that areas with a higher incidence of anti-Japanese movements and victims of the April 3rd incident had a higher prevalence of heat-related illnesses. This confirmed that the environmental characteristics of Jeju Island were responsible for the majority of heat-related illnesses in the Gujo-eup and Jocheon-eup areas. Based on these findings, it was concluded that the occurrence of direct heatwave victims, namely heat-related illness patients, is influenced not only by meteorological factors but also by a complex interplay of social, environmental, and individual temperament factors. Consequently, it is suggested that instead of a uniform approach to heatwave damage reduction implemented by the government, region-specific and systematic mitigation measures tailored to each locality are necessary.