The Sentencing Project provides research and advocacy for prison reform, and the organization's latest report examines recent nationwide incarceration trends. The site tracked the number of people in prison per state from 1999-2013.
Two-thirds of states experienced a modest decline during those years while the rest continued to see rises in their prison populations. The site notes "the overall pace of change, though, is quite modest given the scale of incarceration."
Furthermore, The Sentencing Project adds:
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.
The full data is available here.
