Although the vast majority of immigrants in California came here legally, the state still has by far the largest undocumented immigrant population in the country, many of whom are young. In fact, it’s estimated that as many as 350,000 young undocumented immigrants living in California are eligible for deferred deportation and work authorization, as a result of the Obama administration’s recent policy shift, according to the Migration Policy Institute.

And while the rate of growth has slowed significantly over the past three decades, the population of undocumented immigrants in California is still far more than 2.5 million strong. – about 8 percent of the state’s total population, according to a report by the Public Policy Institute of California. As of 2008, undocumented immigrants made up more than 10 percent of the populations of Santa Clara, Monterey/San Benito, Imperial, and Napa Counties.

The majority come from Mexico, and the heaviest concentrations are based in urban and major agricultural regions.

Because there are no national or state level surveys that count undocumented foreign-born residents, the data are only indirect population estimates. PPIC used tax returns (filed with Independent Taxpayer Identification Numbers) and corroborated data with recent estimates from The Pew Hispanic Center and the Department of Homeland Security.

Click on each county below for the estimated number of undocumented immigrants throughout California (based on 2008 estimates). The darker the shade of red, the larger the number of undocumented residents in that region.

Map data sources:

• Counting California’s Unauthorized Immigrants (Public Policy Institute of California)

• U.S. Census Bureau

Unauthorized Immigrants in California and all other states (1980 – 2008)

Source: Public Policy Institute of California via Passel and Woodward (1984); Warren (2011)