WASHINGTON. The number of illegal immigrants living in the U.S. shrank 8 percent to 11.1 million in 2009 from a peak of 12 million in 2007, a period when border enforcement was tightening and the economy unraveling, a new report says. The yearly average of illegal immigrants arriving in the country from March 2007 to March 2009 fell two-thirds from the inflow from March 2000 to 2005.