PROJECT SUMMARY It is well-documented that where you reside in America shapes when you die, and this has been shown to be particularly true among low-income Americans. These place-based inequalities in health have grown over time in the United States, driven by increased mid-life mortality due to drug- and alcohol-related deaths and suicides. While the drivers of this rise in mid-life mortality are complex and multifactorial, there is broad consensus that the adoption of evidence-based treatments for substance use disorder and mental illness has the potential to improve health and save lives. Despite their effectiveness, behavioral health services are generally thought to be underused, with very limited access to these services in some regions of the country. We study the drivers of place-based inequities in the Medicaid program, the primary source of insurance coverage and payer of behavioral health services for low-income populations. This application seeks to understand whether and to what extent place-based inequalities in mid-life mortality — and their gradients by gender and race/ethnicity — are driven by the causal effects of place on access to evidence-based behavioral healthcare treatment by studying the low-income population on Medicaid. Because families sort into areas based on a wide range of factors — e.g., economic opportunity, amenities, cost-of-living, etc. — if people predisposed to poor (or good) health outcomes tend to cluster in particular localities then observed health differences between areas may reflect this non-random sorting (or “selection”) rather than the causal effects of place. To address this challenge, we use a quasi-experimental movers research design that follows otherwise similar Medicaid enrollees residing in the same place that move to different destinations. Subsequent differences in their healthcare utilization and health can be attributed to place effects if movers are observed for a period of time before the move to adjust for baseline outcomes. Second, to better under social gradients we stratify by sociodemographic characteristics and recover the effects of places for distinct groups —comparing differences in the impacts of a place on different groups reveals whether it tends to narrow or widen inequalities. Finally, we examine whether place-based effects correlated with immutable characteristics of areas (e.g., climate) or features that are more readily amenable to policy intervention (e.g., the healthcare delivery system). We make an original contribution, by advancing the understanding of the relationship between “place” and health for low-income populations, with a focus on understanding the role of differential access to high-quality, behavioral healthcare services.