E.g., 03/02/2024
E.g., 03/02/2024
Unauthorized Migrants Living in the United States: A Mid-Decade Portrait

Unauthorized Migrants Living in the United States: A Mid-Decade Portrait

Unauthorized migration, especially unauthorized migration originating in Mexico, remains a "lightning rod" issue in the United States, often galvanizing public opinion and attracting the attention of U.S. policymakers, especially during times of slow job growth.

Major concerns have always been that unauthorized migrants undercut wages, particularly among unskilled workers, and that the unanticipated enrollment of their children in large numbers at local schools raises educational costs and disrupts instructional programs. Recently added to this list are issues of national security.

Where the Numbers Come From
Most U.S. surveys do not ask people whether they are living or working in the United States illegally. Consequently, nearly all current estimates of the size and characteristics of the unauthorized migrant population use what is called the "residual method."

The residual method estimates the unauthorized population as the total number of foreign-born counted in the survey or census minus an estimate of the legally resident immigrant population based on birth, death, and legal immigration statistics. The resulting figures are then further adjusted for the degree of underenumeration of the unauthorized population in the census or survey.

Using the same logic, these estimates can be further broken down into age, sex, country-of-origin, and year-of-entry sub-groupings. The residual method works reasonably well because in-depth studies show that the vast majority of unauthorized migrants do in fact respond to surveys and therefore are represented in official U.S. statistics along with the legally resident foreign born. The 2004 numbers presented here are based on the residual method. 

Even more detailed estimates of the characteristics of unauthorized migrants have come from new methods that estimate the probability of unauthorized status of the foreign born in surveys or censuses based on characteristics that are known to be associated with legal versus unauthorized status (e.g., naturalization status, welfare receipt, occupation). The estimates of education, income, state settlement and migration, and poverty presented here were estimated using this method. 

Detailed estimates of the characteristics and duration of stay of unauthorized Mexican migrants have also come from surveys of Mexican migrants living in the U.S. and former U.S. immigrants living in Mexico that ask directly the terms of entry into the U.S. (see Massey, Durand, and Malone 2002). Some of the information about the circular nature of Mexican migration discussed here has come from this project.

In contrast, other observers believe the work unauthorized migrants perform in often undesirable jobs is vital to the operation and health of the U.S. economy. Such differences of viewpoint derive in part from varying perceptions about how many unauthorized migrants come to the U.S., how long they stay or remain unauthorized, how many children they have, and their level of economic disadvantage. Good answers to these questions are thus critical to the immigration debate.

It is not easy to count or describe accurately the unauthorized population, and differences of opinion become exacerbated when estimates based on erroneous assumptions or faulty methodologies enter the public domain.

For example, early estimates made during the 1970s were extrapolated from the number of illegal border crossings from Mexico to the United States. Researchers today know that these estimates were much too high because they failed to take into account the fact that many unauthorized migrants make multiple trips, even within a single year, meaning that each new border crossing does not result in an additional unauthorized migrant living in the country.

However, through careful analysis and triangulation of multiple data sources, including U.S. and international census and survey data and birth, death, and legal immigration records, researchers can construct quite consistent pictures of the size, growth, and characteristics of the unauthorized migrant population in the United States. We describe here the most up-to-date and systematically assembled assessments currently available, many of them based on recent work we have carried out.

Population Size

In 2004, the foreign-born population in the United States reached 35.7 million persons, comprising approximately 12 percent of the United States population. Of this group, estimates indicate approximately 10.3 million — 29 percent of the foreign born — were unauthorized migrants (see Figure 1).

The remaining legally resident foreign-born group includes naturalized citizens (32 percent), legal permanent residents who have not yet become citizens (29 percent), refugees (7 percent), and temporary legal residents — such as those with temporary visas such as foreign students, temporary workers, and diplomats (three percent).

Figure 1: Foreign Born in the U.S. by Status


The unauthorized migrant population grew appreciably during the 1990s and the first half of the 2000 to 2010 decade. Approximately 3.5 million unauthorized migrants were living in the U.S. in 1990. This number increased to 8.5 million by 2000, which implies an average increase of about 500,000 per year during the 1990s.

Since 2000, the rapid pace of growth has continued despite slow job growth and tighter security at the U.S.-Mexico border. With the population estimated at 10.3 million in 2004 — an increase of 1.8 million since 2000 — the average annual growth during the first half of the 2000 to 2010 decade is estimated at 450,000, only slightly lower than during the late 1990s.

It is important to understand that these figures represent net increases in the unauthorized migrant population. More than 500,000 unauthorized migrants arrive in the United States each year. Roughly 750,000 unauthorized migrants came to the United States during the late 1990s, and 700,000 came annually between 2000 and 2004.

However, these large numbers are offset by an estimated 200,000 to 300,000 unauthorized migrants who leave the United States, die, or become legal immigrants each year. Unauthorized migrants may gain legal status through several routes, including being sponsored by a close relative who is a U.S. citizen or legal immigrant, being sponsored by an employer, or being admitted (under special circumstances) as an asylee or refugee.

Evidence from surveys of immigrants living in the United States and Mexico strongly suggest — at least among Mexicans — that migration to the United States is not a one-time event but typically consists of multiple trips back and forth across the U.S.-Mexico border.

In addition, new estimates of foreign-born emigration based on analysis of the Current Population Survey (a survey conducted in the United States by the U.S. Census Bureau) indicate that Mexicans and unauthorized migrants have among the highest emigration rates, yet they are also more likely to subsequently return to the United States. Although many eventually settle in the U.S. permanently, surveys of former unauthorized migrants living in Mexico indicate that significant numbers also end up returning to Mexico.

It is therefore not surprising that very few unauthorized migrants living in the United States are elderly, or that few unauthorized migrants have lived in the U.S. more than 10 years. As of 2000, only seven percent were aged 50 or older and only 22 percent had come to the U.S. before 1990.

Country of Origin

Although the majority of unauthorized migrants come from Mexico, significant minorities come from other countries in Latin America and other regions of the world. As of 2004, nearly six million, or 57 percent of all unauthorized migrants, were born in Mexico (see Figure 2).

Figure 2: Unauthorized Migrants by Region and Country

An additional 2.5 million (24 percent) came from other Latin American countries (with eight percent from El Salvador, Colombia, or the Dominican Republic), 1.0 million (nine percent) from countries in Asia (with eight percent from China, India, Korea, or the Philippines), 600,000 (six percent) from Europe (with three percent coming from the former USSR, the United Kingdom, or Poland), and 400,000 (four percent) from Africa.

The country of origin of unauthorized migrants varies across states. In California and Texas in 2000, more than 70 percent of unauthorized migrants were born in Mexico. In New York, however, the unauthorized population consisted primarily of "Other Latin Americans" and Asians; less than 15 percent came from Mexico and less than 10 percent were from Central America.

Place of Residence and Settlement

Although unauthorized migrants are highly concentrated, they have been dispersing to new areas of the country in recent years. In 1990, nearly half lived in California (45 percent) and 80 percent lived in one of four states that have traditionally been destinations for immigrants (California, Texas, New York, and Florida).

However, by the early 2000s, one-quarter lived in California and slightly more than half (54 percent) lived in one of the four immigration states. Increasingly, both legal and unauthorized migrants have been settling in or moving to other areas of the country, and, in the case of Mexican migrants, to areas outside the traditional border receiving states.

Unauthorized Mexican migration in particular increased substantially in "new destination" states, places where it had not previously been prominent. For example, the unauthorized migrant populations in Georgia, North Carolina, Tennessee, and Arkansas grew five- to six-fold during the 1990s.

Arizona, which has received tremendous publicity for its unauthorized migration problems, saw its unauthorized population increase by 250 percent during the 1990s. However, Arizona is not unusual in this respect, as the state ranks 26th among the 50 states and the District of Columbia in the rate of growth in unauthorized migrants.

Age and Sex

Young adults ages 18 to 29 are overrepresented among unauthorized migrants. Whereas 16 percent of natives and 19 percent of legal migrants are between the ages of 18 and 29, 34 percent of unauthorized migrants fall in this age category (see Figure 3).

In contrast, children and the elderly are underrepresented among unauthorized migrants. In 2000, only two percent of children in the U.S. were unauthorized migrants. However, 5.2 percent of children — 60 percent of whom are U.S.-born — lived in families headed by unauthorized migrants.

Children are underrepresented not because immigrants have lower fertility, but because most of their children are not immigrants but rather are born in the United States.

Figure 3: Unauthorized Migrants and Natives by Age

The sex ratio of the unauthorized migrant population is not as skewed as one might imagine given the common depiction of unauthorized migrants as primarily male sojourners seeking temporary work. Unauthorized migrants are only slightly more likely to be male (54 percent) than legal immigrants (48 percent) or natives (49 percent).

Education, Employment, and Poverty

According to new analyses of the 2000 Census, the educational attainment of unauthorized migrants tends to be lower than that of legal immigrants and natives. Among 18- to 24-year-olds, the proportion without a high school diploma or GED is nearly twice as high (54 percent) as legal immigrants (27 percent) and more than three times the level of natives (15 percent).

Labor force participation levels among male unauthorized migrants come within five points of natives; 85 percent of unauthorized men ages 25 to 44 are in the labor force compared with 90 percent of natives. However, unauthorized women have much lower levels of labor force participation; only 55 percent of unauthorized women ages 25 to 44 are in the labor force compared with 76 percent of natives.

Unauthorized migrants are not as concentrated in low-level agricultural jobs as commonly thought. In 2000, only 4.2 percent were working in agriculture, while 13 percent were in construction, 16 percent in leisure/hospitality, and 20 percent in manufacturing; 11.5 percent were working in professional or managerial occupations.

Given their generally low levels of educational attainment and female labor force participation levels, it is not surprising that the average family income is much lower and poverty levels high among unauthorized migrants compared to either natives or legal immigrants.

Poverty levels among children living in unauthorized migrant families are more than twice as high (38 percent)as among those living in native families (17 percent), and 80 percent higher than among children in legal immigrant families (21 percent).

Looking Ahead

Will the unauthorized migrant population continue to grow at the present pace? In the short run, this seems highly likely. Despite tightened border security and restrictions on the legal and social rights of unauthorized migrants, the unauthorized migrant population has continued to grow at a rapid pace during the post-September 11 era.

Furthermore, the unauthorized migrant population is no longer concentrated in only a few industries or a few parts of the country. Rather, unauthorized migrants have become increasingly integrated in all sectors of the economy throughout the nation; there appears to be widespread demand for their labor.

Finally, the circular migration pattern of unauthorized migrants between Mexico and the U.S., the pattern of working in the United States while maintaining homes and family ties in Mexico, and the ease of international communication and travel, suggest a high level of social and economic integration between Mexico and the U.S. that would be extremely difficult to disentangle.

The long-term future is more difficult to predict, and may depend in part on the economic development of the countries and regions of the world from which unauthorized migrants originate. Research suggests that heightened aspirations and opportunities for upward mobility abroad, rather than desperate poverty, lead to high levels of international migration.

As has occurred in the past for other countries that once sent many immigrants to the U.S., migration from developing countries such as Mexico may diminish as opportunities for upward mobility become more readily available in these developing countries.

For More Information:

Bean, Frank D. and Gillian Stevens. 2003. America's Newcomers and the Dynamics of Diversity, Russell Sage: New York.

Massey, Douglas S., Jorge Durand, and Nolan J. Malone. 2002. Beyond Smoke and Mirrors: Mexican Migration in an Era of Economic Integration. Russell Sage: New York.

Passel, Jeffrey S. 2005. "Unauthorized Migrants: Numbers and Characteristics." Background Briefing Prepared for Task Force on Immigration and America's Future. Pew Hispanic Center. Available online.

Passel, Jeffrey S., Jennifer Van Hook, and Frank D. Bean. 2004 . "Estimates of Legal and Unauthorized Foreign Born Population for the United States and Selected States, Based on Census 2000." Sabre Systems, Inc. Available online.

Van Hook, Jennifer, Weiwei Zhang, Frank D. Bean, and Jeffrey S. Passel. 2004. "Foreign-born Emigration: New Approaches and Estimates Based on Matched CPS Files," Demography (forthcoming).