This article shows that most immigrants to the US are legal.
It states: “Border crossings don’t even account for a majority of the people joining the unauthorized population in a given year. In fiscal 2016, for instance, the Department of Homeland Security estimated 628,799 people who had previously entered the country legally overstayed their visa that year. Other groups, such as the Center for Migration Studies, have similarly estimated that visa overstays account for about two-thirds of the total number of people joining the undocumented population in any given year.
“The number attempting to get across the Southern border is probably the lowest it’s been since at least the 1970s,” said Robert Warren, a demographer with the Center for Migration Studies. “I’m surprised the [Trump] administration hasn’t really focused on overstays. That’s where the action is.””