Unauthorized Aliens Residing in the United States: Estimates Since 1986
Prepared for Members and Committees of Congress
Estimates derived from the March Supplement of the U.S. Census Bureau’s Current Population
Survey indicate that the unauthorized resident alien population (commonly referred to as illegal
aliens) has risen from 3.2 million in 1986 to 11.1 million in 2005. The estimated number of
unauthorized aliens had dropped to 1.9 million in 1988 following passage of a 1986 law that
legalized several million unauthorized aliens. About two-thirds of the unauthorized population in
Similarly, the Department of Homeland Security’s Office of Immigration Statistics (OIS) reported
an estimated 11.6 million unauthorized alien residents as of January 2006, up from 8.5 million in
January 2000. The OIS based its estimates on estimates from the U.S. Census Bureau’s American
Community Survey. The OIS estimated that the unauthorized immigrant population in the United
States increased by 37%, with an annual average increase of 515,000 unauthorized aliens over the
past six years.
Research suggests that various factors have contributed to the increase in unauthorized resident
aliens in recent years, and that the rise is often attributed to the “push-pull” of prosperity-fueled
job opportunities in the United States in contrast to limited or nonexistent job opportunities in the
sending countries. Some observers maintain that lax enforcement of employer sanctions for hiring
unauthorized aliens has facilitated this “push-pull,” but it is difficult to demonstrate this element
Some researchers are now suggesting that the increased unauthorized resident population is an
inadvertent consequence of border enforcement and immigration control policies. They posit that
strengthened border security has curbed the fluid movement of seasonal workers. They also cite
the backlog in processing immigrant petitions, which some argue lead aliens to risk residing
without legal status with their family in the United States while they wait for the petitions to be
processed or visas to become available.
Some observers point to more elusive factors when assessing the increase of unauthorized
resident aliens—such as shifts in immigration enforcement priorities away from illegal entry to
removing suspected terrorists and criminal aliens, or discussions of possible “amnesty”
legislation. Others argue that border security measures enacted in recent years have not received
adequate funding to be effective against unauthorized migration.
This report does not track legislation and will be updated as needed.
Backgr ound ..................................................................................................................................... 1
Estimates Since 1986.......................................................................................................................2
Analysis from the Current Population Survey.................................................................................4
Analysis from the American Community Survey............................................................................6
Figure 1. Estimated Number of Unauthorized Resident Aliens, 1986-2005...................................3
Figure 2. Unauthorized Resident Alien Population by Place of Origin, 1986 and 2005.................5
Figure 3. Unauthorized Resident Aliens in 2005, by Reported Year of Arrival..............................6
Author Contact Information............................................................................................................8
An estimated 37 million foreign-born people reside in the United States. In recent years, the
United States typically admitted or adjusted 600,000 to 1 million aliens annually, giving them the
status of “legal permanent resident” (LPR), a term synonymous with the term immigrant. In
addition to those foreign nationals who permanently reside legally in the United States, millions
each year come temporarily on nonimmigrant visas, and some of these nonimmigrants (e.g.,
foreign students and intra-company business transfers) may reside legally in the United States for
several years. It is also estimated that each year hundreds of thousands of foreign nationals 1
overstay their nonimmigrant visas.
The three main components of the unauthorized resident alien population are (1) aliens who
overstay their nonimmigrant visas, (2) aliens who enter the country surreptitiously without
inspection, and (3) aliens who are admitted on the basis of fraudulent documents. In all three
instances, the aliens are in violation of the Immigration and Nationality Act (INA) and subject to
The last major law that allowed unauthorized aliens living in the United States to legalize their
status was the Immigration Reform and Control Act (IRCA) of 1986 (P.L. 99-603). Generally,
legislation such as IRCA is referred to as an “amnesty” or a legalization program because it
provides LPR status to aliens who are otherwise residing illegally in the United States. Among
IRCA’s main provisions was a time-limited legalization program, codified at § 245A of the
Immigration and Nationality Act, that enabled certain illegal aliens who entered the United States 2
before January 1, 1982, to become LPRs. It also had a provision that permitted aliens working 3
illegally as “special agricultural workers” to become LPRs. Nearly 2.7 million aliens established
legal status through the provisions of IRCA.
Continued high levels of unauthorized migration to the United States have, in part, prompted the
current discussion of guest worker programs, as well as major proposals that would permit
legalization under specified conditions. There are also proposals aimed at reducing unauthorized 4
migration by tightening up enforcement of immigration laws. The report of the National
Commission on Terrorist Attacks Upon the United States (also known as the 9/11 Commission)
stated that “more than 9 million people are in the United States outside the legal immigration
system” as one of the reasons for the Commission’s recommendations to improve immigration 5
services and strengthen enforcement of immigration laws.
This CRS report presents data estimating the number of unauthorized aliens who have been living
in the United States since 1986. There have been a variety of estimates of the unauthorized
resident alien population over this period, sometimes with substantially different results. This
report is limited to data analyses of the Current Population Survey (CPS) conducted by the U.S.
1 See CRS Report RS22446, Nonimmigrant Overstays: Brief Synthesis of the Issue, by Ruth Ellen Wasem.
2 8 U.S.C. § 1255a.
3 8 U.S.C. § 1160.
4 For a discussion of proposals in the previous Congress, see CRS Report RL33125, Immigration Legislation and
Issues in the 109th Congress, by Andorra Bruno et al.
5 For a discussion of these recommendations, see National Commission on Terrorist Attacks Upon the United States,
The 9/11 Commission Report, chap. 12.4, pp. 383-391, July 2004.
Census Bureau and the Bureau of Labor Statistics so that there is a basic standard of comparison 6
For a basis of comparison, Figure 1 presents the estimate of 3.2 million unauthorized resident
aliens in 1986 calculated by demographers Karen Woodrow and Jeffrey Passel, who worked for
the U.S. Census Bureau at that time. As expected after the passage of IRCA, the estimate for 1988 7
dropped to 1.9 million. According to demographer Robert Warren of the former Immigration and
Naturalization Service (INS), the estimated unauthorized resident alien population grew to 3.4 8
million in 1992 and to 5.0 million in 1996. By the close of the decade, the estimated number of
unauthorized alien residents had more than doubled. Passel, now at the Pew Hispanic Center,
estimated the unauthorized population in 2000 at 8.5 million, but this latter estimate included 9
aliens who had petitions pending or relief from deportation.
6 The demographers who conducted these analyses used some variant of a residual methodology to estimate the
population (i.e., the estimated population remaining after citizens and authorized aliens are accounted for), another
reason they were selected for this comparison. Demographers at the U.S. Census Bureau also have used a similar
methodology to estimate the residual foreign born population in the 2000 decennial census, and they reported the
following: “According to our calculations, the estimated residual foreign-born population counted in the 2000 census
was 8,705,419. Assuming a 15-percent undercount rate yields a population of 10,241,669 in 2000.” They point out that
the category of residual foreign born includes “quasi legal aliens” (i.e., aliens without legal status who have petitions
pending or court cases underway that potentially would give them LPR status), as well as unauthorized aliens, and thus
should not be considered an official estimate of unauthorized resident aliens. U.S. Census Bureau, Population Division
Working Paper 61, Evaluating Components of International Migration: The Residual Foreign Born, by Joseph M.
Costanzo, Cynthia Davis, Caribert Irazi, Daniel Goodkind, and Roberto Ramirez (June 2002).
7 Karen Woodrow and Jeffrey Passel, “Post-IRCA Undocumented Immigration to the United States: An Analysis
Based on the June 1988 CPS,” in Undocumented Migration to the United States, by Frank D. Bean, Barry Edmonston,
and Jeffrey Passel (RAND Corporation, 1990).
8 Annual Estimates of the Unauthorized Immigrant Population Residing in the United States and Components of
Change: 1987 to 1997, by Robert Warren, Office of Policy and Planning, U.S. Immigration and Naturalization Service,
9 U.S. Congress, House Committee on the Judiciary, Subcommittee on Immigration and Claims, Hearing on the U.S.
Population and Immigration, August 2, 2001.
Figure 1. Estimated Number of Unauthorized Resident Aliens, 1986-2005
1986 1988 1990 1992 1996 2000 2002 2004 2005
Woodrow and PasselWarren
Revised WarrenPassel, Capps, and Fix
Hoefer, Rytina, and CampbellPassel
Sources: CRS presentation of analysis of Current Population Survey data conducted by Karen Woodrow and
Jeffrey Passel (1986 and 1990); Robert Warren (1996, 2000, and 2003); Jeffrey Passel, Randy Capps, and Michael
Fix (2002); Passel (2000, 2005, and 2006); and Michael Hoefer, Nancy Rytina, and Christopher Campbell (2006).
Subsequently, Warren estimated that there were 7.0 million unauthorized aliens residing in the
United States in 2000. As depicted in Figure 1, he also revised his earlier analyses using the latest
CPS and estimated that there were 3.5 million unauthorized aliens living in the United States in
pending or relief from deportation) from his estimates. By 2002, the estimated number of 11
unauthorized resident aliens had risen to 9.3 million. During the first decade after IRCA,
researchers projected that the net growth in unauthorized aliens had averaged about 500,000
annually; more recent analyses estimated the average growth at 700,000 to 800,000 annually. If
the later trend held, about 12 million unauthorized aliens may have been residing in the United 12
States by the close of 2006.
10 U.S. Immigration and Naturalization Service, Estimates of the Unauthorized Immigrant Population Residing in the
United States, 1990 to 2000, January 31, 2003.
11 The Urban Institute, Undocumented Immigrants: Facts and Figures, by Jeffrey Passel, Randy Capps, and Michael
Fix, January 12, 2004.
12 Pew Hispanic Center, Estimates of the Size and Characteristics of the Undocumented Population, by Jeffrey Passel,
March 21, 2005.
The most commonly cited published estimate based upon the March 2006 CPS is that 11.1
million unauthorized aliens were residing in the United States. According to this analysis by
Passel, Mexicans made up more than half of undocumented immigrants—56 % of the total, or
about 6.2 million. He estimated that 2.5 million (22%) were from other Latin American countries. 13
About 13% were from Asia, 6% from Europe and Canada, and 3% from the rest of the world.
As Figure 2 illustrates, the 2005 distribution by region of origin was similar to Woodrow and
Passel’s analysis of the 1986 data, despite the growth in overall numbers from 3.2 million in 1986
to 11.1 million in 2005. In 1986, 69% of the unauthorized aliens residing in the United States
were estimated to be from Mexico, compared with 56% in 2005. Asia’s share of the unauthorized
alien residents appeared to have grown over this period (from 6% to 13%), as did the portion
from the “other” parts of the world. Note that Canada is grouped with North and South America 14
(excluding Mexico) in 1986 and with Europe in 2005.
Passel estimated the number of persons living in families in which the head of the household or
the spouse is an unauthorized alien was 14.6 million as of March 2005. Passel also reported that
in 2005 there were an estimated 1.8 million children who were unauthorized and an estimated 3.1
million children who were U.S. citizens by birth living in families in which the head of the family
or a spouse was unauthorized. He projected that unauthorized aliens accounted for about 4.9% of
the civilian labor force in March 2005, or about 7.2 million workers out of a labor force of 148 15
13 Pew Hispanic Center, Size and Characteristics of the Unauthorized Migrant Population in the U.S.: Estimates Based
on the March 2005 Current Population Survey, by Jeffrey Passel, March 7, 2006.
15 For a discussion of how many unauthorized aliens are currently in the U.S. workforce, see CRS Report RL32044,
Immigration: Policy Considerations Related to Guest Worker Programs, by Andorra Bruno.
Figure 2. Unauthorized Resident Alien Population by Place of Origin, 1986 and 2005
Source: CRS presentation of analysis of Current Population Survey data conducted by Karen Woodrow: Jeffrey
Passel (1990), and Jeffrey Passel (2006).
According to Passel, the largest share of the unauthorized population (4.4 million aliens) had been
in the country five years or less. As Figure 3 depicts, about two-thirds of the unauthorized 16
population were estimated to have entered the United States during the decade 1995-2005.
16 Pew Hispanic Center, Size and Characteristics of the Unauthorized Migrant Population in the U.S.: Estimates Based
on the March 2005 Current Population Survey, by Jeffrey Passel, March 7, 2006.
Figure 3. Unauthorized Resident Aliens in 2005, by Reported Year of Arrival
Source: CRS presentation by analysis of Current Population Survey data conducted by Jeffrey Passel (2006).
Michael Hoefer, Nancy Rytina, and Christopher Campbell of the Department of Homeland
Security’s (DHS’s) Office of Immigration Statistics (OIS) recently published its 2006 estimates of
the unauthorized resident alien population and yielded results consistent with Passel’s, discussed
above. OIS demographers Hoefer, Rytina, and Campbell drew their estimates from the American 17
Community Survey of the U.S. Census Bureau. The OIS reported an estimated 11.6 million
unauthorized alien residents as of January 2006, up from 8.5 million in January 2000. The OIS
estimated that the unauthorized immigrant population in the United States increased by 37% over 18
the past six years, with an average increase of 515,000 annually.
17 The American Community Survey (ACS) is a national sample survey that consists of non-overlapping samples from
which the U.S. Census Bureau collects monthly household data over the course of a year. The OIS demographers stated
that they selected the ACS for the estimates because of its large sample size, 3 million households in 2005 compared to
99,000 for the March 2006 Current Population Survey.
18 Department of Homeland Security, Office of Immigration Statistics, Estimates of the Unauthorized Immigrant
Population Residing in the United States: January 2006, by Michael Hoefer, Nancy Rytina, and Christopher Campbell,
According to the OIS, California had more unauthorized residents than any other state—an
estimated 2.8 million unauthorized aliens in 2006. Texas followed with 1.6 million, and Florida
had 980,000. Among the 10 leading states of residence of the unauthorized population in 2006,
OIS reported that those with the largest average annual increases since 2000 were Texas (91,667),
California (53,333), and Georgia (45,000). The states with the greatest percentage increases in
unauthorized immigrants from 2000 to 2006 were Georgia (123%), Washington (65%), and 19
The research points to various factors that have contributed to the increase in unauthorized
resident aliens. Historically, unauthorized migration is generally attributed to the “push-pull” of
prosperity-fueled job opportunities in the United States in contrast to limited or nonexistent job 20
opportunities in the sending countries. Some observers maintain that lax enforcement of
employer sanctions for hiring unauthorized aliens has facilitated this “push-pull,” but it is difficult
to demonstrate this element empirically. Political instability or civil unrest at home is another
element that traditionally has induced people to risk unauthorized migration, but the motives for
such migrations are sometimes mixed with the economic hardships often correlated with political 21
Although most policy makers have assumed that tighter border enforcement would reduce
unauthorized migration, some researchers are now suggesting that the strengthening of the
immigration enforcement provisions, most notably by the enactment of the Illegal Immigration
Reform and Immigrant Responsibility Act of 1996 (IIRIRA), may have inadvertently increased 22
the population of unauthorized resident aliens. This perspective argues that IIRIRA’s increased
penalties for illegal entry, coupled with increased resources for border enforcement, stymied what
had been a rather fluid movement of migratory workers along the southern border; this in turn
raised the stakes in crossing the border illegally and created an incentive for those who succeed in 23
entering the United States to stay.
Another contributing factor—best represented by the “quasi-legal” aliens discussed above—is the
wait-times for immigrant petitions to be processed and visas to become available to legally come
to the United States. There are statutory ceilings that limit the number of immigrant visas issued
each year. There are also significant backlogs in processing petitions because of the high volume
of aliens eligible to immigrate to the United States and the large number eligible to become U.S.
19 Op. cit. For alternative analyses, see Pew Hispanic Center, Estimates of the Unauthorized Migrant Population for
States based on the March 2005 CPS, by Jeffrey Passel, April 26, 2006.
20 For further analysis, see CRS Report RL32982, Immigration Issues in Trade Agreements, by Ruth Ellen Wasem.
21 For a summary of this research, see Commission for the Study of International Migration and Cooperative Economic
Development, Unauthorized Migration: An Economic Development Response, Appendix E, July 1990.
22 For trends in apprehensions of unauthorized aliens, see CRS Report RL32562, Border Security: The Role of the U.S.
Border Patrol, by Blas Nuñez-Neto.
23 For analysis of the IIRIRA’s effect on unauthorized alien residents, see Wayne Cornelius, “Death at the Border:
Efficacy and Unintended Consequences of U.S. Immigration Control Policy,” Population and Development Review,
vol. 27, no.4 (December 2001). For an analysis of the reduction in unauthorized alien apprehensions after IRCA, see
Thomas J. Espenshade, “Undocumented Migration to the United States: Evidence from a Repeated Trials Model,” in
Undocumented Migration to the United States, by Frank D. Bean, Barry Edmonston, and Jeffrey Passel (RAND
citizens. Of the pending cases, reportedly almost 2 million are immediate relative and family 24
preference petitions. Many observe that these family members sometimes risk residing without
legal status with their family in the United States while they wait for the petitions to be processed
or visas to become available.
Some observers point to more elusive factors—such as shifts in immigration enforcement
priorities away from illegal entry to removing suspected terrorists and criminal aliens, or
discussions of possible “amnesty” legislation—when they assess the increase of unauthorized
resident aliens. Others argue that border security measures enacted in recent years have not
received adequate funding to be effective against unauthorized migration, and some maintain that
state and local law enforcement officers have not been sufficiently involved in apprehending 25
illegal aliens. Some would make illegal presence an aggravated felony. Still others assert that
there has not been sufficient funding and staffing for enforcement of immigration laws in the 26
interior of the country. It is difficult to measure whether, or to what extent, these other
phenomena have contributed to the increase in unauthorized resident aliens.
Ruth Ellen Wasem
Specialist in Immigration Policy
24 For analysis of immigration admissions, visa priority dates, and backlogs, see CRS Report RL32235, U.S.
Immigration Policy on Permanent Admissions, by Ruth Ellen Wasem.
25 For a full discussion of these issues and legislative options, see CRS Report RL34204, Immigration Legislation and
Issues in the 110th Congress, coordinated by Andorra Bruno.
26 For a summary of recent funding, see CRS Report RL34004, Homeland Security Department: FY2008
Appropriations, by Jennifer E. Lake et al.