"In December 31, 2010, state and federal correctional authorities had jurisdiction over 1,605,127 prisoners, a decrease of 9,228 prisoners from yearend 2009. The combined U.S. prison population decreased 0.6% in 2010, the first decline since 1972. The 2010 imprisonment rate for the nation was 497 sentenced prisoners per 100,000 U.S. residents, which is 1 in 201 residents. The statistics in this report are drawn from the Bureau of Justice Statistics' (BJS) National Prisoner Statistics (NPS) series, which annually collects data on prisoner counts and characteristics, as well as admissions, releases, and capacity, from the 50 states and the Federal Bureau of Prisons. The 2010 NPS collection is the 85th in a series begun in 1925."
Bureau of Justice Statistics: http://www.bjs.gov/