As far as I can see this does not say what the undocumented prisoners were incarcerated for. However, it does say that about 27% of the crimes in the report were immigration offenses. It therefore seems likely that most of the undocumented people incarcerated and charted are charged with immigration offenses.

Immigration offenses that result in federal prison are primarily deported illegal criminal offenders who reenter the country illegally. Foreign nationals with no criminal record who walk across our borders are not sent to federal prison. The largest percentage of federal inmates serving time for drug trafficking is Latinos.

Michael, your first sentence reinforces the point being made by fuzzy11: undocumented people are a disproportionate part of the federal prison population at least in part because they are the only ones being imprisoned on immigration offenses. (The US Sentencing Commission reports, for FY 2017, that over 20,000 persons were sentenced to an average of 12 months federal imprisonment for immigration offenses. I sincerely hope that 100% of that population is non-citizens, and it roughly accounts for well over 10% of the federal prison population (though we have a stock/flow issue with this simplistic accounting).)

Your other data may be a valid way to make the case non-citizens commit more crimes than citizens, but using the federal prison population to make the case is highly problematic. Indeed, your reference to federal drug trafficking provides further reason to question reference to federal prison populations because the feds give particular attention to cross-border trafficking and will often actively pursue non-citizens (e.g., El Chapo).

Again, I am not taking issue with your desire to prove a broader point, just with heavy emphasis on the federal prison population to try to do so.

The federal prison population is the focus of the DOJ report and it was worth posting. It is an indicator but not proof of crimes committed by illegals. The term "immigration offenses" has often been misinterpreted to include foreign nationals who have done nothing more than cross the U.S. border illegally. Notwithstanding U.S. Code § 1325, everyone knows that those people do not go to federal prison. If they are caught, previously deported criminal aliens and illegals smuggling drugs or people, or committing other prison-eligible crimes go to prison. Another widely-used diversion is to lump illegal immigrants with legal immigrants and assert that immigrants are a low crime contingent.
Fortunately, the Washington Post report I cite compares illegal and legal immigrants to demonstrate that, at least in Texas, illegals are far more dangerous as a group than legal immigrants. With regard to homicides in Texas, people have been murdered by illegals that the current system was unable to keep from crossing our border. In my book, preventable deaths are a serious problem. I concede your point that a timely report on the number of illegals housed in state prisons, and for what offenses, would provide the best perspective.

Michael, I think your point and concern with combining legal immigrants and illegal immigrants is well taken. I would expect and hope that legal immigrants are particularly disinclined to commit crimes for fear or losing their legal status and being deported. But if is it true that legal immigrants are particularly inclined to be law abiding (even relative to the native-born), in turn there may be a public safety/crime-reduction advantage in enabling some path to citizenship for those who are now here illegally.

There is at least one other factor to discuss beyond the public safety component, which seems to be the only issue being brought up.

What about societal cost? How much are we spending to identify, apprehend, and incarcerate these individuals? Unless we decide to cede all claims of being a nation, which means protecting our borders, we have no choice but to keep them out whether they are otherwise criminals or not.

It costs about $33,000 per year X 37,200 illegals in prison. If my math is right, that’s $1.2 billion just for the incarceration part and does not include enforcement, use of public services, etc.

That alone makes it imperative to solve the problem without even considering how many are dangerous criminals.