Estimates of the number of unauthorized immigrants living in the United States put this population at around 11 million in 2010 (Passel and Cohn, 2011), which is about 30 percent of the foreign-born population and over 5 percent of the U.S. workforce.2 While approximately 6.1 million are from Mexico, representing 55 percent of the total, other countries contributing substantially to the undocumented population include Brazil, China, Ecuador, El Salvador, Guatemala, Honduras, India, Korea, and the Philippines (Hoefer et al., 2012; Passel et al., 2012). The number of unauthorized residents originating from Mexico is more than 10 times larger than the number of unauthorized residents from any other country. Between 1999 and 2009, Mexican men aged 15 to 50 years old accounted for three-fourths of all apprehensions at the U.S.–Mexico border, and Mexican women aged 15 to 50 years old accounted for an additional one-seventh of apprehensions. The remaining apprehensions are distributed among juvenile Mexican nationals, senior Mexican nationals, and migrants from other countries. Reconciling the rates of apprehensions by nationality and gender with the estimates of the stocks of illegal residents in the United States requires analyses that are beyond the scope of this report.

Data on illegal immigrant flows are even harder to come by than estimates of the stock. Still, changes in the stock of illegal immigrants should roughly capture net flows, once attrition and deaths are subtracted and an upward adjustment is made for the household survey undercount.3 For instance, the unauthorized immigrant population increased in net terms by about 500,000 annually during the early 2000s. After allowing for undercount, mortality, and return migration, the inflow of unauthorized immigrants was estimated at around 850,000 per year during the period 2000 to 2005 (Passel and Cohn, 2010).

Unauthorized immigration slowed considerably during the U.S. housing bust and subsequent recession as unemployment rates soared (Passel and Cohn, 2009a). Return migration may also have increased. As a result, the unauthorized immigrant population decreased slightly between 2007 and 2009 and has since stabilized (Hoefer et al., 2012; Passel and Cohn, 2011). Falling immigration and rising returns were most evident in the Mexican case. According to the Mexican Census, 1.4 million Mexicans and their children left the United States between 2005 and 2010, about the same as the number who are estimated to have entered the country (Passel et al.,


2 Of the 11 million unauthorized immigrants, 8 million are estimated to be in the labor force (Passel and Cohn, 2011).

3 The limitations of U.S. household surveys in measuring the unauthorized population are discussed in Chapter 4.

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