Actually, 40 percent might be too low
The key research on "overstays" -- the working term for this group of unauthorized immigrants Ramos had in mind -- was undertaken in 1997 by the U.S. Immigration and Naturalization Service. The INS estimated that overstays accounted for 41 percent of the undocumented.
Here we’ll add a bit of complexity. Immigration researchers divide the undocumented into two groups -- overstays and "entries without inspection." The first group might have a student, temporary work or tourist visa. The second group never went through any review.
Robert Warren -- who helped with that work at the INS and now is a senior fellow at the Center for Migration Studies, a research group founded by Catholic missionaries -- told PunditFact that not only does the balance between the two still hold, it has likely tilted toward the overstays.
"Since 2000, arrivals from Mexico, who are about 85-90 percent 'entries without inspection,' have plummeted, while overstays have increased, or stayed at about their historical levels," Warren said.
Warren said the shift likely stems from U.S. efforts that have made it harder to enter by land.
He sent us this graph from his latest research at the center.