A new study by the Center for Immigration Studies (CIS), found that 30.8 million immigrants (legal and illegal) have settled in the U.S. since 1990. Their U.S.-born children and grandchildren total 12 million. Thus immigration has accounted for 42.8 million more people in the U.S. during the past 29 years. That total is greater than the combined population of 22 states, and accounts for one in eight residents of this country.
Supporters of mass immigration often that it is necessary in order to increase the working-age population and thereby sustain Social Security and Medicare. But the CIS study found that this has not been happening, one reason being that the the average age immigrants is increasing. The addition of immigrants and their progeny since 1990 has only increased our working-age population (16-64) from 63.9 percent to 64.4 percent.
Read more at cis.org