By Patricia Zapor • Catholic News Service • Posted February 20, 2013

WASHINGTON (CNS) — A new study concludes that there are about 11.7 million of what it calls unauthorized immigrants in the U.S., 4 million more than in 2000.

In a report released Feb. 15, the Center for Migration Studies, a New York-based educational institution also quantified why residents of some states, particularly in the Southeast, have perceived a significant growth in the number of immigrants around them.

Seven Southern states with the fastest growing population of undocumented immigrants each saw the number of such immigrants increase by more than 11 times between 1990 and 2010. The study explained that nationwide, about 18 percent of the foreign-born population was undocumented. The percentage in those seven states was about that as well in 1990.

But in 2009, in those states about 47 percent of their foreign-born residents were unauthorized to be here, the study found. They got more immigrants overall, and a higher percentage of them were undocumented.

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“In 1990, the foreign-born population in the seven states was small, about 500,000, and fewer than one in five were unauthorized residents,” the study published in the International Migration Review said. “But by 2010, the foreign-born population had quadrupled to 2.6 million and nearly half of them were unauthorized.”

The study was co-written by Robert Warren, former demographer for the Immigration and Naturalization Service and John Robert Warren, sociology professor at the University of Minnesota.

The pair described in detail their approach to counting undocumented immigrants and how it differs or is complemented by other widely used counts. Because immigrants who are in the country without permission arrive by a variety of legal and illegal ways, and generally strive to remain unnoticed, coming up with an accurate count of how many there are is a challenge. Schools, social service agencies and city planners, among others, all nevertheless need to have some idea of who might require their services, the report notes.

And with Congress weighing immigration reform legislation that could include a path to legalization and citizenship for those who are here without legal status, planning for how to process them will require a good sense of who’s in the country and where they live.

The report says their estimate of 11.7 million unauthorized immigrants does not differ markedly from other recent estimates that are based on similar data and calculation methods.

“However,” it adds, “our estimates allow unique assessments of trends over time in the size of that population and of the component processes generating those trends.”

For example, the two Warrens, who are father and son, said their methods allowed them to show that the declining number of undocumented immigrants occurred not just because fewer people entered the U.S. because of a weaker economy and border crackdowns, but because the number of unauthorized immigrants “departing from the population is large and increasing.”

The annual number of unauthorized immigrants moving to the U.S. increased steadily in the 1990s, from about 550,000 in 1993 to 1.1 million in 1999, and more than a million each year through 2000, then declined to as few as 400,000 in 2009, they said.

The pair estimate that between 1990 and 2009 about 7.5 million people left the unauthorized population, that includes those who legalized their status, were deported, died or moved away voluntarily.

More than half of all undocumented immigrants live in California, Texas, Florida and New York, the report said. The inflow and outflow in each of those states roughly matched that of the country as a whole in the 20-year analysis, with 29 states and the District of Columbia finding net losses in undocumented population in 2009.

In the seven states with the fastest growing undocumented populations — Alabama, South Carolina, North Carolina, Tennessee, Arkansas, Kentucky and Georgia — the number of unauthorized immigrants was more than 11 times higher in 2010 than it was in 1990.

The report said those states were home to 2.5 percent of the undocumented population in 1990. By 2010, they had 10.4 percent of the U.S. total, it said.

The Center for Migration Studies was established in 1964 and formally incorporated in 1969 by the Congregation of the Missionaries of St. Charles, Scalabrinians.

It was co-founded and directed over its first several decades by Father Lydio F. Tomasi, now pastor of Holy Rosary Church in Washington, and then-Father Silvano M. Tomasi, who is now an archbishop and the Vatican’s representative to U.N. agencies in Geneva.

The center is a legally distinct, tax-exempt agency with an independent board of trustees.