 According to the Pew Research Center, in 2007 the number of unauthorized Mexican immigrants peaked at 6.9 million and has dropped by more than 1 million to an estimated 5.6 million in 2014.After the Great Recession, more immigrants actually returned to Mexico rather than migrated to the United States.From 2009 to 2014, 1 million Mexicans and their families left the U.S. for Mexico.