A combination of drilling, hydrogeochemical survey, geophysical survey, and the numerical modeling for the flow and transport of groundwater was performed to evaluate seawater intrusion in Baeksu-eup, Yeonggwang-gun, Korea. Twelve wells were drilled for the collection of geologic, hydrogeochemical, hydrologic, and geophysical logging data to characterize seawater intrusion. To evaluate the salinity distribution of a coastal aquifer, drilling, geophysical data such as vertical electrical soundings (VES), well logging, and hydrogeochemical results were used. Hydrogeochemical results were used to understand the origin of salt and the seawater mixing ratio of groundwater. Spatial layer interfaces derived from YES data, various in situ physical properties from geophysical well loggings, the estimated equivalent NaCl concentration, and aquifer test such as slug test and so on were used as useful input parameters for the numerical simulation with density-dependent flow. Our multidisciplinary approach for evaluating seawater intrusion can be considered as a valuable attempt to enhance the utilization of various data and the reliability of numerical groundwater modeling.