It's true that rates of enslavement have decreased since the end of the Civil War. But it's disgusting that our common vernacular talks about an institution that ended over 150 years ago when in fact it is still very much alive and generating enormous profits for the people who choose to exploit it.

If you want straight-up hard numbers, I can't recommend any resource more then DrugWarFacts:

http://www.drugwarfacts.org/chapter/race_prison