PurposeTo examine the relationship between youth incarceration in adult correctional facilities and mental health in early adulthood. MethodsWe analyzed nationally representative data from 1997 through 2019 (N = 8,961) using the National Longitudinal Survey of Youth 1997. An ordinary least squares regression model using inverse probability weights was used to assess the influence of youth incarceration in an adult facility on average mental health scores from age 18 to 37. ResultsRespondents incarcerated in an adult facility as a youth had poorer average mental health than those not held in adult prisons or jails over the course of the study period. Those incarcerated for longer in adult facilities also exhibited more mental health symptoms. DiscussionYoung people incarcerated in adult correctional facilities experience poorer long-term mental health related to depression and anxiety in early adulthood.