PURPOSE: This study investigated mental health outcomes among young adults who experienced direct police contact - including unfair or aggressive policing - in the past year. METHODS: Data came from 2019 participants enrolled in the nationally representative 2021 Transition to Adulthood Supplement of the Panel Study of Income Dynamics. Descriptive analyses provided population-based prevalence estimates of police contact measures (including being stopped unfairly, being frisked or searched, and officer verbal or physical aggression) in the overall sample and stratified by key sociodemographic factors. Linear regression models quantified associations between police contact and mental health domains (i.e., psychological distress, depressive symptoms, anxiety symptoms, and well-being), adjusting for sociodemographic factors and participants' history of arrest. RESULTS: Males, lesbian, gay, or bisexual individuals, and those with lower levels of education reported the highest prevalence of frequent police contact (i.e., ≥2 times in a 12-month period). When considering aggressive policing, stark racial disparities emerged, with Black young adults exhibiting the highest prevalence. Net of covariates, more frequent police contact was associated with poorer mental health, with comparable effect estimates observed across all outcome domains. When considering unfair and aggressive policing, experiencing an unfair stop was the most strongly and consistently associated with higher levels of psychological distress (β = 0.44, 95% confidence interval [CI] = 0.00, 0.88), depression (β = 0.48, 95% CI = 0.15, 0.81), and anxiety (β = 0.53, 95% CI = 0.17, 0.90). DISCUSSION: Our findings underscore the need to implement policies and procedures that curtail frequent, unfair, and aggressive policing and surveillance of U.S. young adults - especially in minoritized and underresourced communities.