While the number of people in prison in the United States has stabilized in recent years, incarceration trends among the states have varied significantly. Two-thirds of states (34) have experienced at least a modest decline since 1999, while one-third (16) have had continued rises in their prison populations.
Nine states have produced double-digit declines during this period, led by New Jersey (29% since 1999), New York (27% since 1999), and California (22% since 2006, though partly offset by increasing jail use). These prison population reductions have come about through a mix of changes in policy and practice designed to reduce admissions to prison and lengths of stay. Recent analyses have shown that these substantial reductions have had no adverse effect on public safety.
The overall pace of change, though, is quite modest given the scale of incarceration. The total U.S. prison population declined by 2.4% since 2009. Five of the states with rising prison populations have experienced double-digit increases, led by Arkansas, with a 17% rise since 2008. While sharing in the national crime drop, these states have resisted the trend toward decarceration. And of those states with declining prison populations, 16 have had less than a 5% decline since their peak years. The decline in the federal prison population has been of this magnitude: 1% since 2011.
Just as mass incarceration has developed primarily as a result of changes in policy, not crime rates, so too have declines reflected changes in both policy and practice. These have included such measures as drug policy sentencing reforms, reduced admissions of technical parole violators to prison, and diversion options for persons convicted of lower-level property and drug crimes.
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