Medical debt is a critical challenge to Americans’ financial stability and well-being. We use unique Urban Institute credit bureau data on more than 10 million consumers to investigate (1) where people are more likely to have medical debt in collections and (2) which county-level socioeconomic and health characteristics predict medical debt. We find that 79 out of the 100 counties with highest levels of medical debt in collections are in states that have not expanded Medicaid under the Affordable Care Act. These counties are mostly concentrated in Georgia, North Carolina, and Texas. We also find that a county’s prevalence of chronic conditions is the strongest predictor of medical debt in collections. In addition, counties with high shares of uninsured, low-income, or Black populations have higher rates of medical debt in collections. We offer a few insights on policies that can reduce medical debt, such as Medicaid expansion and consumer protections through the No Surprises Act.