Reported are findings from five studies which explored the special problems and needs of the developmentally disabled offender in the Illinois criminal justice system. Introductory information includes a discussion of the problem, goals of the present study, and a review of programs for retarded offenders throughout the U.S. Presented are five studies based on interview and questionnaire data collected from law enforcement officers, judical personnel, correctional institutions, developmentally disabled offenders (50 case studies), and community agencies serving the mentally retarded, the cerebral palsied, and the epileptic person. Among findings revealed are that police officers in Illinois do not have the training to detect symptoms of developmental disability; that judical personnel support community based programs and special institutions as alternatives to prison for developmentally disabled offenders; and that community agencies tend to provide developmentally disabled offenders services such as referral and recreation rather than more expensive services such as special living arrangements or training. Recommendations stemming from each study are outlined such as the need to standardize the definition of mental retardation within the judicial system and to train correctional personnel to identify and work with the retarded. Appendixes consist primarily of research instruments used in the studies. (LS)