South Korea’s population is declining and its composition changing, associated with lowest-low fertility rates and rapid aging (super aging). When estimating changes in future exposure to extreme heat events (EHE), events that are predicted to be intensified due to climate change, it is important to incorporate demographic dynamics. We analyze business-as-usual (BAU) population and climate scenarios—where BAU refers to no significant change in current processes and trends in either domain—from 2010 to 2060 for South Korea. Data for both BAU scenarios are spatially linked and used to measure and identify national and sub-national and age-group specific EHE exposure. The results reveal an increasing exposure to EHE over time at the national level, but this varies widely within the country, measured at the municipal level. The most intensive exposure levels will be in the decade ending in 2040 driven by high estimated severe EHE. Sub-nationally, Seoul will be the most vulnerable municipality associated with super aging, while severe EHE not demographic factors will be relevant in Daegu, the second-most vulnerable metropolitan area. By 2060, national estimates suggest the older population will be up to four times more exposed to EHE than today. While the population of South Korea will decline, the rapid aging of the population ensures that specific regions of the country will become exceedingly vulnerable to EHE.