A unified earthquake catalog for South Korea and its surroundings was developed, containing 63 298 events. Four declustering methods, including Gardner–Knopoff, Reasenberg, Uhrhammer, and Marsan, were compared to identify the mainshocks. The catalog offers a reliable database for seismic hazard assessments and seismotectonic studies. It fills gaps in previous studies, providing an up-to-date catalog for accurate seismic risk assessment and future earthquake forecasting in the region.