A new social indicator measures the use of incarceration by juvenile justice systems. When combined with 1-day custody rates, it provides a comprehensive picture of State juvenile corrections systems in both static and dynamic terms. When combined with prevalence measures of juvenile crime and responses to these crimes, estimates of the prevalence of State juvenile corrections custody can help provide a more accurate portrait of delinquency and juvenile justice, from offense and arrest through adjudication and commitment. Prevalence estimates of State juvenile corrections custody can be directly compared with the probabilities of other significant and traumatic life events for juveniles, such as serious injury, illness, or accident. These prevalence figures can be used with data from the National Correctional Reporting Program to estimate the lifetime probabilities of various groups' entrances into State custody. Finally, this research is made possible for the first time by the availability of age, race, sex, and first-occasion (e.g., commitment) data produced as part of a national data collection program, referred to as the Juveniles Taken Into Custody Research program (JTIC). 7 tables, 4 figures, and 14 references