This study is to provide guidance for selecting sites suitable for offshore wind farm developments with lower social, economic, and environmental impacts in the South Korea southwest coastal area with its complicated shoreline configuration, large ecologically important tidal flats, and various marine-based human activities. To analyze the economic feasibility of offshore wind farms, harvestable energy was calculated using an InVEST (Integrated Valuation of Environmental Services and Tradeoffs) model that has been used widely for marine ecosystem service analysis. Capital costs for grid connection and electricity transmission, operation and maintenance costs, and other costs were integrated together to calculate a net present value (NPV) of a 60-MW offshore wind farm assuming a lifetime of 20 years of operation. It is important to note that NPVs of offshore wind farms are affected significantly by the proximity to the closest inland substations, showing the importance of grid connection. Criteria that may cause social and environmental conflicts were grouped into three categories: nature conservation and landscape protection, marine-based human activities, and marine environment and marine ecosystem. Available datasets for each category were compiled and incorporated into GIS-based maps. Many social and environmental criteria overlapped spatially, and areas influenced by one or more criteria were designated as areas of potential conflicts. Economic analysis results and potential social and environmental conflicts were considered together to select areas that could produce wind energy more efficiently with minimum social and environmental conflicts. Economic, social, and environmental assessment strategies and procedures provided in this study can be used as an effective decision-making support tool to find sites for offshore wind farm development and various other offshore developments as well.