This study aims to propose a systematic approach for offenders with mental illness through an analysis of the U.S. Sequential Intercept Model (SIM) and the limitations of fragmented approach toward offenders with mental illness in South Korea. This study analyzes Sequential Intercept Model (SIM) in U.S. (community, police, prosecution, correctional facilities and courts, post-release agency, and probation) into three parts: 1) concepts and objectives, 2) key components, and 3) case studies. In addition, the study highlights similarities, differences, and key contents between each stage in SIM. Moreover, there is comparison and evaluation of various agencies in South Korea dealing with mentally ill offenders using SIM framework. To manage mentally ill offenders effectively, there is 4 principles 1) service based on the therapeutic jurisprudence, 2) training for professional intervention, 3) partnerships with various agencies, 4) peer support. Sequential and comprehensive intervention for mentally ill offenders is not only beneficial for them, but also essential for minimizing social costs and increasing public safety.