Juvenile crimes have serious consequences for individuals, families, and society as a whole. Youth in the juvenile justice system may have complex mental health needs that require coordination of multiple systems. Oftentimes those needs are not adequately addressed because resources are limited, and care, fragmented. In recent years, many community-based rehabilitative approaches have been identified, some showing positive outcomes associated with reduced long-term recidivism, improved family functioning and school performance. Despite the potential benefits of those interventions, key system questions remain unanswered. For example, what capacity is needed to deliver the interventions? What effect would they have on the crime in a community as well as on the life course of young offenders? No single economic study can completely assesses all of the key questions surrounding complex systems like these. This article presents a discrete-event simulation model that simulates youth passing through the juvenile justice system, mental health system, and the community. Drawing data from multiple sources, the model links quality of the mental health screening tool, access to treatment, service use, criminal outcomes, and service capacity together and assesses how various policies decide and are being shaped by the dynamics between various system features. The results provide insight for policy makers to allocate constrained resources while maximizing the public health benefits of the programs. Meanwhile, the model demonstrates an innovative approach to integrate existing evidence and evaluate the economic impact of policies regarding mental health in juvenile justice.