Running Out of Inmates? Cohort Nonreplacement and the Approaching End of Mass Incarceration

The US prison population is declining at an accelerating rate. Based on a review of research in the age–period–cohort framework, current declines in crime and incarceration are driven primarily by cohort nonreplacement: Each successive generation has entered adulthood with substantially lower propensities for criminal involvement than the high-crime cohorts of the 1980s and 1990s. Although tough sentencing policy for many years delayed the decline of imprisonment after crime started falling, the aging out of high-crime birth cohorts and the aging in of low-crime cohorts nearly guarantee accelerating rates of decarceration, at least for the near future. We use data from the National Corrections Reporting Program to predict that US prison admission rates will fall by an additional 50% within two decades, approaching the imprisonment levels last seen in the 1970s. We also address what we call the “orphan fact” of American criminal justice: the dramatic decline in Black imprisonment rates. In the conclusion, we set forth a research agenda to address the fundamental questions emerging in the era of significantly reduced crime and incarceration and build on the progress made to date.