This issue brief summarizes our research findings on the factors related to geographic variation and the growth of the child Supplemental Security Income (SSI) program. Our analysis is the first to exploit county-level variation in caseloads over time for insights on the determinants of child SSI caseloads. We find health and economic variables explain a significant share of the variation in SSI receipt across counties. However, we also find that changes in these factors explain only a quarter of the growth in child SSI rates nationally from 2003 to 2011, and the influence of these health and economics factors varies substantially by state and region. This points to the need for state-specific studies to shed light on the different factors driving SSI growth across states.