The local sources of regularly collected and publicly available data on probation, conditional discharge, supervision, and periodic imprisonment of adult offenders include the Illinois circuit courts, county probation departments, the Administrative office of the Illinois Courts, and the Cook County Clerk's Office of the Circuit Court and the Adult Probation Department. The Federal sources include the Administrative Office of the United States Courts and Federal officials (judges, clerks, and probation officers) operating locally in Illinois. In addition, specialized data is available from such sources as the Supreme Court Committee on Probation Services Assessments, statewide surveys, and probation information from the Center for Legal Studies. Problems concerning data availability include the lack of the data needed for studies focusing on specific sentencing phenomena, and difficulty in obtaining the individual case files which are located at the courts and with probation officials throughout the State. Therefore, recommendations include conducting exploratory and descriptive studies before more focused studies are undertaken, and the use of individual case file data for the research of specific sentencing phenomena. The plans for improvement of data sources, statistical data, and references are included. A total of 10 appendixes include guidelines for access and dissemination of the data, circuit listings, a list of Illinois County Sheriff's Offices, and probation assessments in Illinois counties.