experts pointed to the economic downturn and the resulting high unemployment as factors behind the shift . `` The recession has had a significant effect on immigrants ' decisions on whether to come to the U.S. , '' said Michelle Mittelstadt , director of communications at the nonpartisan Migration Policy Institute . Would-be unauthorized immigrants and legal temporary workers are mostly the ones who have decided to stay put in their home countries for now , Mittelstadt said . The largest declines in the foreign-born population were in states that were hardest hit by the recession , including California , Florida and Arizona . Mittelstadt noted , however , that those immigrants already in the United States appear to be staying . A recent study by the Pew Hispanic Center concluded that emigration from Mexico , the largest source of immigrants to the United States , slowed at least 40 percent between mid-decade and 2008 , based on national population surveys in the United States and Mexico , as well as Border Patrol apprehension figures . The Mexican-born population in the United States dropped by about 300,000 between 2007 and 2008 , according to census data . The new Census
-LRB- CNN -RRB- -- After nearly 40 years of recorded increases , the number of immigrants living in the United States remained flat between 2007 and 2008 , recent statistics released by the U.S. Census Bureau show . The number of naturalized citizens in the U.S. increased , partly attributed to voter drives for the 2008 election . According to the Census Bureau 's American Community Survey , the U.S. foreign-born population represented about 12.5 percent of the population in 2008 , down from 12.6 percent in 2007 . Taking into account the margin of error , it was possible that the immigrant population remained even . `` Between '07 and '08 there really was n't that much of a change , '' said Elizabeth Grieco , chief of immigration statistics staff at the Census Bureau . But given the steep upward trend in the foreign-born population since 1970 , no change is big news . The American Community Survey collects data from about 3 million addresses each year , and provides one of the most complete pictures of the population , according to the bureau . The survey does n't give a reason for the leveling off , but