Here is some more - including race AND citizenship. Note that Mexicans make up 17% of the population in Federal Prisons.

http://www.bop.gov/news/quick.jsp

I also found some data on IQ for Texas Prisons that seems to suggest IQs are below the mean, but not by much.

http://www.laits.utexas.edu/txp_media/html/just/features/0504_01/slide2.html