From ThePeoplesVoice.org:

7.3 million in the US prison system

Link: http://wsws.org/articles/2009/mar2009/pris-m04.shtml

A study released this week by the Pew Center on the States delivers a staggering statistic: 7.3 million Americans – or 1 in every 31 adults – are in the nation’s prison system. This figure includes those in US jails and prisons, on parole, on probation, or under other forms of correctional supervision. No other country comes close to matching this number. If these individuals were grouped together, they would number more than the entire populations of Israel or Honduras, or all of the residents of Washington state.