I worked in the federal prison system in Arizona and another state that was not near the border. The federal prison in Arizona had an illegal alien population closer to 40%. I toured several state prisons in Arizona and they were close to 50%.  There were also INS prisons not directly under control of the BOP which had 100% illegal aliens in detention. 

I knew people who worked in prisons, both state and federal in Texas, New Mexico and California. The population breakdowns were about the same.  Illegal aliens in these prisons are there for violent crimes for the most part, those who are just picked up for illegal entry are not housed in prisons but are in temporary detention centers.

Every Hispanic prisoner in prison is a member of a violent gang.  Surenos, Mexican Mafia, MS-13 to name a few.  Every single one of them is gang affiliated.