I couldn't find anything more recent.
As of December 31, 2007, there were 2,293,157 prisoners held in federal or state prisons or in local jails according to the U.S. Department of Justice (source).
59 prison murders and 6,750 assaults, fights, rapes, etc., out of a population of approximately 2.29 million -- pretty much proves my assertion that it is a MYTH that other prisoners will do violence to child molesters/killers.