"During 2007, the prison population increased more rapidly than the U.S. resident population. The imprisonment rate — the number of sentenced prisoners per 100,000 residents — increased from 501 prisoners per 100,000 U.S. residents in 2006 to 506 prisoners per 100,000 U.S. residents in 2007. From 2000 through 2007, the imprisonment rate increased from 475 per 100,000 U.S. residents to 506 per 100,000 U.S. residents. During these seven years, the number of sentenced prisoners increased by 15% while the general population increased by 6.4%."
Sabol, William J., PhD, and West, Heather C., Bureau of Justice Statistics, Prisoners in 2007 (Washington, DC: US Department of Justice, December 2008), NCJ224280, p. 1.