Last week Cato published a new immigration research and policy brief called “Criminal Immigrants: Their Numbers, Demographics, and Countries of Origin” that estimates the illegal immigrant incarceration rate—a subject long avoided in academic and policy research circles due to data limitations. 

Our headline finding is that both illegal immigrants and legal immigrants have incarceration rates far below those of native-born Americans—at 0.85 percent, 0.47 percent, and 1.53 percent, respectively. Excluding illegal immigrants who are incarcerated or in detention for immigration offenses lowers their incarceration rate to 0.5 percent of their population—within a smidge of legal immigrants. As a result, native-born Americans are overrepresented in the incarcerated population while illegal and legal immigrants are underrepresented, relative to their respective shares of the population. 

The relatively low number of incarcerated illegal immigrants places some immigration restrictionists in an uncomfortable position: choosing which myth to believe. The first myth is that illegal immigrants are especially crime-prone. The second myth is that there are actually two to three times as many illegal immigrants as is commonly reported. The usual number used by the government and most demographers is that there are 11 to 12 million illegal immigrants in the United States but a steady drumbeat of skeptics claim the real number is about 22 to 36 million. 

No matter how you dice the numbers, a larger illegal immigrant population in the United States means that their incarceration rate is even lower that what we report. Without adjusting for age, a total illegal immigrant population of 22 million would lower their incarceration rate to 0.56 percent using Cato’s estimate of the size of the incarcerated illegal immigrant population. Using the higher (and sillier) 36 million illegal immigrant population estimate by Ann Coulter lowers their incarceration rate to 0.34 percent. 

For the sake of argument, let me assume you do not like Cato’s numerical estimate of incarcerated illegal immigrants and you would prefer to use another estimate. The America American Survey form S2601B (2014 1‑year sample) reports that there were 157,201 non-citizens in adult correctional facilities in 2014. That is the absolute maximum possible number of illegal immigrants incarcerated in that year. Using the ACS estimate lowers the illegal immigrant incarceration rate to 0.71 percent if the population is an estimated 22 million and to 0.44 percent if their total population is 36 million. 

Immigration restrictionists cannot have it both ways. They cannot assume that illegal immigrants are super-criminals and that their population in the United States is several times higher than it really is. No matter how you dice the numbers, their incarceration rate falls as their estimated population increases. For consistency’s sake, it’s time for immigration restrictionists to choose which myth they want to believe.