"At yearend 2015, an estimated 6,741,400 persons were under the supervision of U.S. adult correctional systems, about 115,600 fewer persons than yearend 2014. This was the first time since 2002 (6,730,900) that the correctional population fell below 6.8 million. The population declined by 1.7% during 2015, which was the largest decline since 2010 (down 2.1%). Additionally, the decrease was a change from a 3-year trend of stable annual rate declines of about 0.6% between 2012 and 2014. About 1 in 37 adults in the United States was under some form of correctional supervision at the end of 2015. This was the lowest rate observed since 1994, when about 1 in 38 adults (1.6 million fewer persons) were under correctional supervision in the nation. This report summarizes data from several Bureau of Justice Statistics' (BJS) correctional population supervised by adult correctional systems in the United States. These systems include persons living in the community while supervised by probation or parole agencies and those under the jurisdiction of state or federal prisons or in the custody of local jails."
Bureau of Justice Statistics: https://www.bjs.gov/