"For the first time in nearly 40 years, the number of state prisoners in the United States has declined. Survey data compiled by the Public Safety Performance Project of the Pew Center on the States, in partnership with the Association of State Correctional Administrators, indicate that as of January 1, 2010, there were 1,404,053 persons under the jurisdiction of state prison authorities, 4,777 (0.3 percent) fewer than there were on December 31, 2008.1 This marks the first year-to-year drop in the state prison population since 1972.
"In this period, however, the nation’s total prison population increased by 2,061 people because of a jump in the number of inmates under the jurisdiction of the Federal Bureau of Prisons. The federal count rose by 6,838 prisoners, or 3.4 percent in 2009, to an all-time high of 208,118.
"Prior to 1972, the number of prisoners had grown at a steady rate that closely tracked growth rates in the general population. Between 1925 (the first year national prison statistics were officially collected) and 1972, the number of state prisoners increased from 85,239 to 174,379.2
"Starting in 1973, however, the prison population and imprisonment rates began to rise precipitously. This change was fueled by stiffer sentencing and release laws and decisions by courts and parole boards, which sent more offenders to prison and kept them there for longer terms.3 In the nearly five decades between 1925 and 1972, the prison population increased by 105 percent; in the four decades since, the number of prisoners grew by 705 percent.4 Adding local jail inmates to state and federal prisoners, the Public Safety Performance Project calculated in 2008 that the overall incarcerated population had reached an all-time high, with 1 in 100 adults in the United States living behind bars.5"

Source

Pew Center on the States, "Prison Count 2010: State Population Declines for the First Time in 38 Years," (Washington, DC: The Pew Charitable Trusts, April 2010), p. 2.
https://www.ncjrs.gov/App/Pub…
http://www.pewtrusts.org/en/r…