Many strategies for preventing and containing the spread of COVID-19 require wide-scale public cooperation backed by informal social control. Yet, fear of infection may either motivate or impede individuals’ willingness to intervene when they observe others flouting the rules. This study aims to evaluate how the risk of exposure to COVID-19 in the immediate residential setting affects an individual’s willingness to exercise informal social control in the neighborhood. Using longitudinal household survey data collected before and during the COVID-19 pandemic in Hong Kong, respondents were linked to confirmed cases of COVID-19 through spatiotemporal information to measure their risk of exposure to COVID-19. The findings show that the risk of exposure to COVID-19 in individuals’ immediate residential setting had weakened informal social control and that this relationship was mediated by neighborhood social cohesion. Our findings reveal how public health crises alter the social behavior of residents and neighborhood dynamics in an urban setting, emphasizing the need for policies that foster social cohesion and strengthen community resilience.