Although there is little difference in rates of marijuana use between White and Black youth, Blacks have significantly higher rates of marijuana use and disorder in young adulthood. Theory suggests that factors tied to social disadvantage may explain this disparity, and neighborhood setting may be a key exposure. This study sought to identify trajectories of marijuana use in an urban sample during emerging adulthood, neighborhood contexts that predict these trajectories and social role transitions or "turning points" that may redirect them. Data are from a longitudinal cohort study of 378 primarily Black emerging adults who were first sampled in childhood based on their residence in low-income neighborhoods in Baltimore City and followed up annually. Group-based trajectory modeling identified three groups: No Use (68.8%), Declining Use (19.6%), and Chronic Use (11.7%). Living in close proximity to an alcohol outlet, and living in a neighborhood with more female-headed households and higher rates of violent crime increased the odds of membership in the Chronic Use group relative to No Use. Living in a neighborhood with more positive social activity increased the odds of membership in the Declining Use group relative to No Use. Not receiving a high school diploma or GED, pregnancy, and parenting also increased the odds of membership in the Declining Use group relative to No Use. These findings provide support that minority youth living in socially toxic and disordered neighborhoods are at increased risk of continuing on a trajectory of marijuana use during emerging adulthood while positive social activity in neighborhoods has the potential to redirect these negative trajectories. Besides taking on the responsibilities of parenting, emerging adults in the marijuana user groups had similar educational and family outcomes, suggesting that early marijuana use may have long-term implications.