In response to increases in Illinois prison population during the late 1980s and early 1990s, low rates of access to substance abuse treatment services while in prison, and high rates of recidivism, in August 1995, the Illinois Department of Corrections opened the Southwestern Illinois Correctional Center (SWICC) as a dedicated substance abuse treatment facility operating under a modified therapeutic community philosophy. The 600-bed minimum security facility for incarcerated adult male inmates operated since 1995 as a prison-based drug treatment program, and was modified and enhanced beginning in October 2006 to include more extensive vocational training, a specialized methamphetamine treatment unit, more sophisticated pre-release planning and mandatory post-release aftercare. This evaluation examines the implementation of these enhanced services and the impact of this new enhanced treatment model at SWICC on recidivism since July 2006, and is the result of a collaborative effort between researchers from Loyola University Chicago, the Illinois Department of Corrections, the Illinois Criminal Justice Information Authority, Treatment Accountability for Safe Communities (TASC), the Safer Foundation, and Community Education Centers (CEC). The report focuses on four years of operation, covering the period from July 1, 2006 through the end of State Fiscal Year 2010 (June 30, 2010).