As the U.S. Department of Homeland Security continues to pour money into border security, evidence is emerging that illegal immigration flows have fallen to their lowest level in at least two decades, reports the Washington Post. The nation's population of illegal immigrants, which more than tripled, to 12.2 million, between 1990 and 2007, has dropped by about 1 million, say demographers at the Pew Research Center. A key and largely overlooked sign of these ebbing flows is the changing makeup of the undocumented population. Until recent years, illegal immigrants tended to be young men streaming across the Southern border seeking work. Data show that the typical illegal immigrant now is much more likely someone who is 35 or older and has lived in the U.S. for a decade or more.