It's difficult to tally a population that lives in the shadows, but new data from the Public Policy Institute of California (PPIC) estimates that 2.7 million immigrants are living illegally in California. That's more than any other state in the nation.
The majority of California's undocumented immigrants arrive from Latin America, and specifically Mexico.
Laura Hill, a senior fellow at PPIC, expects that trend to continue.
"As long as there's still a big wage disparity between Mexico and the United States, or any neighboring country, or any country that's it's possible to get to from the United States, there will be a pull for some folks to make that move," says Hill.
She says the majority of people immigrating illegally are men who are seeking work.
But, she says unauthorized immigrants are all ages, and come from all over the world -- including Asia, Canada and Europe.
Nearly every county in the state has an unauthorized population.
PPIC reports that Los Angeles County has the most at more than 800,000, followed by Orange County (250,000), Santa Clara County (180,000), and San Diego County (170,000). There are about 80,000 undocumented immigrants living in the greater Sacramento region.
The Pew Hispanic Center reports that nearly one in ten workers in California is undocumented. Undocumented immigrants work predominantly in the hospitality industry (30 percent), construction (21 percent) and production (15 percent).