Falling Prison Populations Alone Don't Prove Decarceration, New Dataset Reveals

Updates to online data mapping tool show differences in states’ jail and prison trends 

New York, NY—The Vera Institute of Justice today announced several updates to its Incarceration Trends Project online data tool, which collects and analyzes information on current jail populations and historic trends in every U.S. county. The tool now includes comprehensive state-level incarceration data. By including prison incarceration trends alongside jail trends, the true trajectory of mass incarceration and the impact of reform efforts become clear. What it demonstrates is that falling prison population rates alone do not always indicate that a state is curbing its use of incarceration, and likewise, rising prison rates do not always mean that the state’s use of incarceration is growing.

The update shows that from 2006 to 2014, jail and prison trends mirrored each other in most states, but diverged in 16 states:

  • In seven states, average daily jail populations continued to rise while prison populations declined. In two of these states (Iowa and South Dakota), the growth of jail populations exceeded the modest declines in these states' prison populations, leading to a net increase in the state’s use of incarceration. In the five other states (Kentucky, Louisiana, Mississippi, North Carolina, and Virginia), growing jail populations have essentially cancelled a portion of the incarceration decline driven by falling prison populations.  
  • In nine states, jail populations have declined while prison populations have risen. In four states (Florida, Idaho, Minnesota, and Oregon) falling jail populations exceeded the prison growth, leading to a net decline in the state’s use of incarceration. In five other states (Arizona, Indiana, Ohio, Pennsylvania, and Wyoming), the falling jail population has slowed each state’s rising incarceration rate that is driven by prison growth.

“Until now, there hasn’t been a nationwide dataset to examine whether, and how, state prison and jail trends relate to one another,” said Christian Henrichson, research director of Vera's Center on Sentencing and Corrections and project lead. “While these data alone cannot explain why trends diverge, it’s now clear that they often do. Policymakers and the public must look at both prison and jail populations to measure the success of reform efforts.”

In addition to newly available jail population data for every state, this update to the Incarceration Trends data tool also provides new data on the county residents in prison, for each county in Ohio and Pennsylvania (in addition to existing data for California and New York)—so that policymakers and the public can examine how decisions made at the local level affect prison growth. 

“Examining the number of county residents in prison and jail puts the difficult problem of 2.2 million Americans behind bars in local context that can inform the conversation on the changes we want in our communities,” said Jacob Kang-Brown, senior research associate.

Complete information on the change in state incarceration rates between 2006 and 2014 is available here.

The Incarceration Trends Project is supported by the John D. and Catherine T. MacArthur Foundation as part of itsSafety and Justice Challenge initiative, which seeks to address over-incarceration by changing the way America thinks about and uses jails, as well as the Robert W. Wilson Charitable Trust.