Persons with serious mental illnesses (SMI) are involved in the criminal justice system at a disproportionately higher rate than the general population. While the exact causes remain unclear, it is accepted that a comprehensive strategy including mental health treatment is needed to reduce recidivism. This paper describes a unique jail diversion program coordinated by a county prosecutor's office in which individuals were diverted towards mental health services including case management, community-based services, and housing supports. Outcomes were studied over a five-year period, beyond the typical 12- to 24-month follow-up in other studies. Individuals who completed the program, compared to those who did not complete it, were at lower risk for being rearrested, arrested fewer times, and incarcerated fewer days. Gains were moderated by previous criminal justice involvement and substance use but, nevertheless, were maintained despite severity of history. The strongest gains were seen while the individual was still actively enrolled in the diversion services and these outcomes were maintained for up to four years. These findings suggest that completion of a jail diversion program facilitated by a prosecutor's office can lower recidivism and days incarcerated. Further research is needed to assess the unique contribution of prosecutor office facilitation.