Background Federally qualified health centers (FQHCs) are pivotal safety net primary care providers for the medically underserved. FQHCs have complex organizational designs, with many FQHCs providing care at multiple physical locations ("sites"). The number of sites, however, varies considerably between FQHCs, which can have important implications for differential access that may perpetuate disparities in quality of care. Purpose The objective of this study is to explore the organizational and environmental antecedents of the number of sites operated by each FQHC. The findings of this study contribute to a better understanding of FQHCs' expansion that has vital implications for cost and access outcomes. Methodology/Approach The study is based on data between the years 2012 and 2018. Using multivariate growth curve modeling, we analyzed the final sample, consisting of 5,482 FQHC-years. Results The level of competition, measured as the number of FQHC sites in the Primary Care Service Area (PCSA) and the number of primary care physicians per 1,000 PCSA residents, was positively associated with the number of FQHC sites. The number of patients, the level of federal grant, and the year were also positively associated with the number of FQHC sites, whereas percentage of Medicaid patients; workforce supply, measured as primary care physician assistants per 1,000 PCSA residents; Medicaid expansion; and state/local funding available for FQHCs were not. Conclusion Findings of this study indicate that competition, especially between peer FQHCs, is significantly associated with FQHC expansion. Practice Implications This result suggests that FQHC managers and policymakers may closely monitor cost, access, and quality implications of competition and FQHC expansion.