When it comes to people in the country without proper documentation, the majority of them didn’t cross the Mexican border at all. Most of them came to the United States legally — but then don’t leave.
…Visa overstays have outnumbered people who enter the country illegally at the Southern border every year since 2007, according to a report by the Center for Migration Studies. The report’s authors estimate that the number of total visa overstays was 600,000 more than the total number of border crossers and that in 2014, visa overstays accounted for two-thirds of all new undocumented immigrants.
…Those caught by the U.S. government can apply for asylum if they can claim a credible fear that their lives would be in danger by returning to their home countries; some immigrants, in fact, turn themselves in to federal agents to do so. Apprehensions of people attempting to cross the border illegally, however, far outnumber the number of people requesting asylum at the border.
…It is unclear how many of these migrants applied for asylum after arriving in the U.S.[emphasis: Peanut Gallery]— but the total number of asylum cases has been increasing as well.
“A growing percentage of border crossers in recent years have originated in the Northern Triangle states of Central America,” wrote Robert Warren and Donald Kerwin of the Center for Migration Studies. “These migrants are fleeing pervasive violence, persecution and poverty, and a large number do not seek to evade arrest, but present themselves to border officials and request political asylum. Many are de facto refugees, not illegal border crossers,” the authors wrote.