The population of Japan is currently decreasing due to a declining birthrate and an aging population, with a concurrent concentration of people in Tokyo. These factors contribute to regional decline and an increase in depopulated areas. In recent years, it is anticipated that the “related population,” individuals engaged in various aspects of the local community, will play a significant role in regional development. However, there has been little research on the factors influencing attachment formation among these related populations. This study investigates the factors influencing attachment formation to regions among both permanent populations and related populations through surveys. Structural equation modeling of the survey results reveals that a “positive impression of the area” significantly influences “attachment to the area” for both groups.