In 1592, the Japanese hegemon Toyotomi Hideyoshi launched an invasion of Chosŏn Korea. The resulting six-year conflict, known as the Imjin War (1592-1598) involved China, Korea, and Japan and had devastating environmental and geopolitical consequences. Soon after the war, Koreans encountered something just as lethal: severe outbreaks of infectious diseases. In the early seventeenth century, post-war environmental degradation and unfavourable climatic factors created conditions ripe for epidemics, particularly within the North East Asian borderlands between China and Korea. Disease and environmental problems, compounded with socioeconomic hardship, in turn prompted an increase of displaced people from the Korean north who transmitted epidemics along their flight routes. Drawing on historical and geographic analysis, this study examines environmental and social hardships in Chosŏn Korea’s northern borderland during the early seventeenth century, and traces the transmission of epidemics across the post-war Korean peninsula as people were displaced from the north. By studying the relationship between displacement and epidemics, this study adds to current discussions on migration theories in climate mobility research and premodern history of medical geography.