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According to estimates out by Pew Research, L.A. and Orange Counties are home to over 1 million people living here illegally. Nationwide, the number is around 11 million.

But digging into the data yields some interesting facts, says James Hollifield. He directs the Tower Center at 91��Ƭ�S�ϼ� in Dallas and is a Global Fellow at the Woodrow Wilson International Center.

Five key points:

1. The undocumented population is actually going down across the nation. "We have seen a declining number of the undocumented and [one of the] reasons for this is that some people are actually returning, going home, especially a lot of Mexicans. We've seen a surge of people living in the United States in an unauthorized status going back home," said Hollifield. According to the Pew Research Center, the total undocumented population peaked at over 12 million back in 2007 and has since gone down by about a million.
       
2. The undocumented workforce reveals a gap in immigration policy. "The simple fact is that we have a tremendous juncture in terms of what we need for our economy and for what the law provides for in terms of the number of people that can come and work here legally," said Hollifield. "We need a lot of unskilled labor and that niche has been filled, not surprisingly, by unskilled immigrants, especially those coming from Mexico and Central America."
       
3. The right number of visas needed to fill that gap is still under debate. "There have been attempts to propose reforms that would allow us to adjust the number of visas based on the level of demand in different sectors of our labor market. One term that is often talked about is by having so-called 'market triggers' so that you can see when there's a surge in demand in a particular sector, whether it's construction, healthcare or any service industry, that you could allow the numbers to adjust so that you could allow more people to come in," said Hollifield. But, he added, the numbers behind that, and even the concept itself, is hotly contested.
       
4. A significant share of the undocumented population arrived legally to the U.S., but overstayed their visas. "Most of those coming from outside the Western Hemisphere are coming here on visas, perhaps tourist visas, and they are simply overstaying the visas. So you're going to see a much high concentration of non-Latino people in the unauthorized, or undocumented population, who are coming from Africa or Asia, in particular," said Holifield. A Department of Homeland Security report found that out of the 45 million people who have come by air and sea with legal visas, 482,781 individuals, or 1.07 percent, had overstayed in 2015. The country with the highest number? Canada.
       
5. Immigrants tend to lead to an overall gain for the economy, but in certain circumstances, they can affect wages for some workers. "They are increasing economic growth, economic activity, they become consumers so the multiplier effects alone of immigration often dwarf whatever effects they may have on depressing wages. But, in certain sectors, in certain areas, you will find those wage effects – especially where unskilled immigrants are competing with other unskilled immigrants," said Hollifield. One 2015 Harvard study, looking at the wages after Cuban migration in the early 1980s, found a drop of relative wages for some of the least educated workers in Miami.