• In 2014, an estimated 11.3 million unauthorized immigrants were living in the U.S., about 3.5 percent of the nation's population. More than 50 percent were from Mexico and an added 20 percent were from Central America.

• Unauthorized immigrants make up about a quarter of the foreign-born population nationwide.

• The largest portion of the undocumented population live in California -- about 3 million, or more than a quarter in the nation. This includes about 142,000 in Santa Clara County (58 percent from Mexico; 31 percent from Asia) and 57,000 in San Mateo County (50 percent from Mexico; 22 percent from Asia).

• About 70 percent of California's undocumented population comes from Mexico and about 14 percent from Asia; nearly 60 percent of the state's undocumented immigrants have lived in the U.S. 10 years or more, and almost a quarter are age 24 or under. Undocumented immigrants make up about 9 percent of California's labor force.

• Nationwide, more than 2 million undocumented immigrants arrived here as children (more than 500,000 in California, including about 279,000 ages 3-17).

• About 80,000 undocumented youth nationwide are estimated to turn 18 each year and approximately 65,000 of those graduate from high school. An estimated 5 to 10 percent of undocumented high school graduates go on to enroll in an institution of higher education and far fewer graduate with a degree.

• More than 680,000 undocumented youth nationwide have received DACA benefits ("Deferred Action for Childhood Arrivals," see sidebar: "Federal and state laws expand opportunities." LINK). Researchers estimate that nearly 1.5 million undocumented youth in the U.S. are currently eligible for DACA, and another 400,000 children will become eligible in the next few years.

• About 7 percent of K-12 students nationwide (13 percent in California) have at least one unauthorized immigrant parent. Among these students, 79 percent were born in the U.S. About 40 percent of unauthorized immigrants nationwide, 4.1 million, resided with children under 18. About 84 percent of these 4.1 million parents -- about 3.4 million -- resided with at least one U.S.-citizen child under 18. Children residing with the other 16 percent of these parents did not include any U.S. citizens.

• An estimated 200,000 to 250,000 undocumented students are enrolled in college nationwide, or about two percent of all college students, according to the Pew Research Center. In a 2015 UCLA survey (see below) of more than 900 undocumented college students nationwide, the researchers found that participants had resided on average an estimated 14 or more years in the U.S.; more than 70 percent were working while in college; and more than 60 percent had at least one member of their household who is a lawful resident or citizen. The study also found that more than three-quarters report worries about being detained or deported; more than half report personally knowing someone who had been deported, including a parent or a sibling; higher proportions experience significantly elevated levels of anxiety, as compared to their citizen peers; and the vast majority (more than 90 percent) have strong desires to become American citizens if they could.

• In 2013, federal immigration agency Enforcement and Removal Operations made 229,698 administrative arrests in the country's "interior," with Homeland Security Investigations resulting in an additional 11,996 administrative arrests. The U.S. Border Patrol reported an additional 420,789 apprehensions, up from 364,768 in 2012, about 98 percent occurring along the southwest border. For 2013, those figures combined to total more than 616,000 removals and returns. Note: "Removals" (deportations) are the compulsory movement of an unauthorized immigrant out of the United States based on a court order. Once deported, serious criminal consequences attach to any subsequent re-entry without permission. "Returns" are the voluntary movement of a deportable unauthorized immigrant out of the United States and doesn't involve a court order. Most returns are Mexican nationals who have been apprehended by the Border Patrol.

• Last month, the Department of Homeland Security (DHS) issued a long-awaited report on the number of persons suspected of overstaying their visas last year, estimating the amount to be about half a million people, or a little more than 1 percent of the 45 million foreign visitors entering by air or sea for business or pleasure. The report did not account for those traveling by land and thus does not fully account for all overstays.

The report was mandated by federal law in 1997, but efforts to collect the information have been impeded by difficulties in collecting and analyzing the necessary data. This is the first time since 1997 that the DHS has conclusively examined this population, according to the New York Times; the DHS now has systems in place to make similar reports each year.

Prior to this DHS report, immigration experts estimated, based on decade-old data, that between 30-50 percent of all undocumented immigrants now living in the U.S. entered the country with legally valid visas and later became unauthorized by virtue of overstaying their visa's departure date without permission.

Sources:

• Pew Research Center: http://www.pewresearch.org/fact-tank/2015/11/19/5-facts-about-illegal-immigration-in-the-u-s/ and http://www.pewhispanic.org/2014/11/18/chapter-1-state-unauthorized-immigrant-populations/

• Migration Policy Institute: http://www.migrationpolicy.org/article/frequently-requested-statistics-immigrants-and-immigration-united-states and http://www.migrationpolicy.org/data/unauthorized-immigrant-population/state/CA

• U.S. Department of Education Resource Guide: Supporting Undocumented Youth (Oct. 2015): www2.ed.gov

• Public Policy Institute of California: ppic.org

• Educators for Fair Consideration: www.e4fc.org/images/Fact_Sheet.pdf

• UCLA 2015 study, "In the Shadows of the Ivory Tower" about the experiences of undocumented college students nationwide: undocuscholars.org

• New York Times: nytimes.com

• Washington Post: washingtonpost.com