2003 stats:
http://crime.about.com/od/prison/a/bjs040720.htm
State and federal correctional authorities held 90,700 non-citizens at midyear 2003, 2.3 percent more than a year earlier. The federal system held 34,456 non citizens (38 percent of all noncitizen prisoners).
(Considering that the vast majority of illegal aliens convicted of non-violent crimes are merely deported rather than imprisoned, that's an enormous number)
On June 30, 2003, the federal system had 170,461 prisoners, more than any state prison system. Since 1995, the federal system has grown an average of 8 percent per year, compared to an average annual growth of 2.9 percent for state inmates and 4 percent for jail inmates during the same period.
Minorities Make Up 60 Percent of Prison Population
An estimated 12 percent of all black males in their twenties were in jails or prisons last June 30, as were an estimated 3.7 percent of Hispanic males and 1.6 percent of white males in that age group. Sixty-eight percent of prison and jail inmates were members of racial or ethnic minority groups.
Jails — locally operated correctional facilities typically holding inmates sentenced to a year or less as well as people in various stages of the criminal justice system, such as awaiting trial -- added more inmates than new beds in the 12 months preceding June 30, 2003. Still local jails were operating at a national average of 6 percent below their official rated capacities. State prisons were between 1 and 17 percent above rated capacity, and federal prisons operated at 33 percent over capacity at the end of 2002.
White non-Hispanics made up 43.6 percent of the local jail population, blacks 39.2 percent, Hispanics 15.4 percent, and other races (Asians, American Indians, Alaska Natives, Native Hawaiians and other Pacific Islanders) 1.8 percent.