Gyeongui Line Park is an urban park project that the City of Seoul has adopted as a means to revitalize declining neighborhoods. This study aims to analyze the project’s effects on housing prices. Unlike extant hedonic studies, this analysis focuses on revealing the heterogeneous effects of the project by the development process, from inception to completion, to understand when and to what extent the park has influenced housing values in the host neighborhood. Findings indicate that the Gyeongui Line Park project has resulted in generally positive externalities to both apartments and multi-family dwellings, with the magnitude varying by relative locations. The effects differ according to the project’s phase and housing type: in the apartment market, values increased about 15% per 100-m approach to the park, starting with the announcement of the park’s procurement plan in 2006; continued to increase through Phase I completion; then decelerated to 0–3% at the beginning of Phase II construction. For multi-family homes, the project corresponded with positive, but smaller increases on housing values (about 2%) starting with Phase I construction in 2012, with the magnitude remaining at 1–2% from 2012 to the present. Findings from this study and its methodology will be valuable in determining the course of future planning efforts to maximize the positive effects of projects in urban revitalization practice.