While incarceration rates have begun to decline nationally, some states expect to put more prisoners behind bars in coming years.

The Pew Charitable Trusts’ public safety performance project published new state prison population projections Tuesday, providing projections of how numbers of inmates could change over the next four years.

A dozen of the 34 states reporting data expect their prison populations to grow more than 5 percent. The number of inmates housed in Iowa state correctional facilities is slated to climb 16 percent by 2018 -- the largest increase of any state. Wyoming (14 percent) and Alaska (11 percent) also reported larger projected growth.

Overall, the total prison population in states reporting data is expected to swell 3 percent over the next four years. If projections hold true, that means the state imprisonment rate should remain about unchanged when adjusted for population growth.

At least six states expect their prison populations to shrink -- albeit not by much -- in the coming years.

“The fastest [prison population] growing states tend to be those that have not put together bipartisan task forces over the last couple years to tackle their growth,” said Adam Gelb, director of Pew’s Public Safety Performance Project.

State Incarceration Projections

The following table shows projections compiled by Pew for the 34 states reporting data:

SOURCES: State agencies, The Pew Charitable Trusts, Council of State Governments Justice Center, JFA Institute

An earlier Pew analysis found 32 states recording declines in both imprisonment and crime rates since 2008. The trends show, according to Gelb, that prison populations don’t need to expand for crime rates to drop.

States pursed a variety of approaches in recent years that helped to push down or limit prison populations. Some reclassified minor drug and property offenses. Revisions to mandatory minimum sentencing laws also provided judges with greater leeway in sentencing. Georgia, for example, approved a law in 2013 allowing judges to impose shorter sentences for certain sexual and violent offenses when prosecutors and defense attorneys both agree the circumstances don’t fit such longer sentences.

Tight budgets and overcrowded prisons often gave lawmakers incentive to pursue reforms. States weren’t all under the same pressure, though, and many measures weren’t budget-driven, Gelb said.

Regardless of how total prison populations fluctuate in the coming years, the number of aging prisoners will rise as baby boomers grow older. A few states have explored early release programs and other efforts aimed at this demographic group.

Prison facilities in some states with projected growth have already exceeded capacity.

The Bureau of Justice Statistics published updated data earlier this fall comparing numbers of inmates in custody to states’ prison capacities. About half of states reporting data were at 99 percent or more of their operational capacity at the end of last year.

State Prison Capacities

Figures listed below show state inmate populations as a percentage of prison capacity, current as of Dec. 31, 2013.

NOTE: Figures not shown were either unavailable or not reported by states. See appendix table 1 in "Prisoners in 2013" published by BJS for notes on individual states. SOURCE: Bureau of Justice Statistics

Data Definitions

  • Operational Capacity: Number of inmates that "can be accommodated based on a facility's staff, existing programs and services."
  • Rated Capacity: Assigned by rating officials
  • Design Capacity: Refers to how many inmates architects/planners originally intended for facilities