Among the Mexican immigrants who leave the U.S., an estimated 5 to 35 percent are deported while the rest opt to go back voluntarily, often taking U.S.-born children with them. Those who were in the U.S. illegally and returned to Mexico also are increasingly saying they will not try to come back — about 20 percent, compared to 7 percent in 2005.
The Pew estimates come amid heightened attention on immigration in an election year where the fast-growing Hispanic population, now making up roughly 16 percent of the U.S. population, could play a key role. Arizona's law, being challenged by the Obama administration in the Supreme Court, seeks to expand the authority of state police to ask about the immigration status of anybody they stop on the rationale that federal enforcement has largely failed.
Since Arizona's law passed in 2010, five other states — Alabama, Georgia, Indiana, South Carolina and Utah — have passed similar measures.
Steve A. Camarota, director of research at the Center for Immigration Studies, a Washington group that advocates tighter immigration policies, said the latest numbers show that immigration policies do make a difference.
"The bottom line is that immigration is not the weather. It is something that ... can be changed," he said. "The economy is worse but enforcement is also higher, making it more difficult for immigrants to get jobs in states like Arizona. They are now making new calculations and changing their views."
—Illegal Mexican immigrants who have stayed in the U.S. for longer periods of time are now more likely to be sent back by authorities than before. About 27 percent of immigrants sent back had resided in the U.S. for a year or more, up from 6 percent in 2005.
—Despite an increase in Border Patrol agents, apprehensions of illegal immigrants at the U.S.-Mexico border have dropped sharply — from 1 million in 2005 to 286,000 in 2011, a sign that fewer illegal immigrants are trying to enter.
—About 30 percent of all current U.S. immigrants are Mexican born, by far the most from any single country; that's down from its peak of 32 percent in 2004-2009. The next largest share comes from China (including Hong Kong and Taiwan), accounting for 5 percent of the nation's 40 million foreign-born residents.
—A typical Mexican woman is projected to have an average of 2.4 children in her lifetime, compared with 7.3 children in 1960.
—By region, Mexican-born immigrants in the U.S. are mostly likely found in the West (51 percent) and South (33 percent). About 58 percent now live in California and Texas, down from 63 percent in 2000 as immigrants spread out over the past decade in search of jobs in other states.
Associated Press writer Christopher Sherman in McAllen, Texas, contributed to this report.
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