This article examines the relationship between the political fragmentation of cities in metropolitan regions, the distribution of social vulnerability, and the city-level economic and social sustainability strategies they adopt. Strategies emerge from prevailing community norms, and polycentric governance arrangements can support conditions in which both economic and social sustainability strategies emerge as compliments, contrary to the concern that fragmentation spurs zero-sum competition. Combining surveys of U.S. cities with social vulnerability data and text analysis of planning documents, we find that greater fragmentation has a negative impact on the sustainable development strategies cities adopt. However, growth and sustainable development strategies tend to develop alongside social sustainability efforts to address human needs. We conclude that development strategies emerge in polycentric systems in relation to the degree of fragmentation which exists, and that subsequent work should continue to focus on identifying these entropic thresholds in order to effectively address lingering inequities.