New Study Details Estimates of US Unauthorized Immigrant Population

New Study Details Estimates of US Unauthorized Immigrant Population

Census and Other Data Produce
20-year Annual Trends 
for Every State


NEW YORK, NY – The International Migration Review (IMR) has published a study that reports new estimates of the unauthorized immigrant population residing in the United States, by state of residence, for each year from 1990 to 2010. The estimates are based on 2000 and 2010 census data, federal administrative data and a statistical methodology that shows annual trends in arrivals of unauthorized immigrants as well as departures from that population. The paper, Unauthorized Immigration to the United States: Annual Estimates and Components of Change, by State, 1990 to 2010, is co-authored by Robert Warren, former demographer for the US Immigration and Naturalization Service (INS), and John Robert Warren, professor of sociology at the University of Minnesota. It is available on at:

For the total United States and the largest states, the estimates reported in the study are comparable to those produced over the past decade by the US Department of Homeland Security (DHS) and the Pew Hispanic Center. However, these estimates are unique because: a) they show a much longer annual time series (20 years); b) the data and methods used produce estimates with smaller ranges of sampling error, especially for states with small unauthorized populations and c) the estimation procedure yields – for the first time ever – annual trends in the inflow of unauthorized immigration to the United States and to every state.

The reports finds that the number of unauthorized immigrants arriving in the United States peaked at more than one million in 1999 to 2001, and then declined rapidly through 2009. The unauthorized immigrant population reached zero growth after 2007 because arrivals dropped sharply after 2001 and the numbers leaving the population steadily increased. In 2009, 384,314 persons entered the US unauthorized population, and 558,118 left. Thus, even though the United States unauthorized immigrant population has essentially reached zero growth, unauthorized immigration to the United States continues at a significant level.

The new estimates illustrate an important aspect of unauthorized immigration that has typically been overlooked: Significant numbers of unauthorized immigrants leave the population each year. An estimated 15.7 million unauthorized immigrants moved to the United States from 1990 to 2009. However, the population grew by 8.2 million during these years because an estimated 7.5 million left the unauthorized immigrant population. These individuals left voluntarily, were removed by DHS, were adjusted to legal status or died.

Other major findings include:

  • The total US unauthorized immigrant population was estimated to be about 11.7 million in January 2010, about 4 million higher than it was in 2000.
  • Of the total unauthorized immigrant population in January 2010, nearly 3 million, or 25 percent, resided in California. The population in the top seven states of residence combined – California, Texas, Florida, New York, Illinois, New Jersey and Georgia – accounted for nearly two-thirds of the total.
  • Between 2000 and 2009, inflows declined in every state except Mississippi (and Washington, DC). In addition, outflows increased in every state. As a result of these trends, 29 states and Washington, DC experienced net losses in population in 2009.
  • The seven states with the fastest growing populations of unauthorized immigrants over the past two decades, in declining order, were in the southeast: Alabama, South Carolina, North Carolina, Tennessee, Arkansas, Kentucky and Georgia. In each of these states, the unauthorized immigrant population was more than 11 times larger in 2010 than it was in 1990.

Although such analysis is beyond the scope of the study, a variety of factors were mentioned that could explain the sharp reduction in population growth in the past decade, including less favorable US economic conditions after 2000, heightened security for air travel after September 11, 2001, and increased enforcement efforts by DHS. Regardless of the underlying reasons, it is clear that the substantial drop in arrivals after 2000 was the primary contributor to declining unauthorized population growth and to reaching zero growth by the end of the decade. The report provides evidence that the economic downturn in 2008 and 2009 played little or no role in reducing unauthorized population growth through emigration because emigration of the unauthorized population did not increase substantially in those years. However, the economic crisis may have dissuaded unauthorized persons from entering the United States.

The report has a number of implications for US immigration policy. First, the long time series of detailed data for every state should be useful in discussions of immigration reform. Second, even though unauthorized arrivals have dropped significantly since 2000, hundreds of thousands continue to arrive each year. Third, departures from the unauthorized immigrant population should be recognized as an important aspect of demographic change for this group. Fourth, improvements in the data sources are needed to solidify the empirical basis for future estimates. Fifth, the Census Bureau’s American Community Survey, the only basis for similar future estimates, has proven to be a vital resource for deriving these estimates.