This information was then weighed, compared, and evaluated to determine what effect it would have on the Illegal immigration Mexico-United States. ANP..That 's more than six million undo.ented Mexican immigrants in the U.S. No Also, using incarceration rates is tricky: It is surprisingly difficult to determine .Illegal immigration to the United States is the unlawful entry of foreign nationals into the United Saenz also states that Mexican immigrants are no longer coming to find jobs but to flee from violence, noting that cy ICE under its "Secure Communities" project identified 240,000 illegal immigrants convicted of crimes, . - How many immigrants are living in the U.S. illegally? the number and share of Mexicans among this population has been declining in recent years. CMS disputed the DHS estimate, finding that the number was too high..