At the end of calendar year 1999, the prison population was 38 percent over rated capacity, totaling 44,660 inmates in a correctional system designed to hold 32,313 inmates. Another 30,756 offenders were on mandatory supervised release. Since 1990, the prison population in Illinois has increased by more than 62 percent. This large increase has occurred despite the enactment of numerous legislative and DOC programs to reduce prison crowding and to address specific inmate needs. Persistent prison population growth has largely been attributed to two factors: (1) an escalation in the volume and length of prison sentences, especially for violent offenses, has resulted in the long-term accumulation of inmates; and (2) dramatic increases have occurred in the number of lower level drug offenders admitted to prison. Given the demands prison population growth has imposed on the DOC, a reorganization has been implemented to hold correctional staff more accountable for the statewide supervision of inmates within correctional facilities and offenders released to the community. Detailed statistics are provided on prison population trends, length of stay, and sentencing. Supplemental information is appended on determinate and indeterminate sentencing in Illinois and on definitions and data interpretations related to the compilation of statistics in the report. 62 tables and 25 figures