The overall number of unauthorized immigrants in the U.S. has remained relatively unchanged since 2009, according to estimates by the Pew Research Center.

Between 2009 and 2014, Pew said that most states saw no major change in the size of their unauthorized immigrant populations. Those populations in seven states, however, declined during that period mainly because of decreasing numbers of unauthorized immigrants from Mexico.

Pew produced its estimates mainly using data from the U.S. Census Bureau.

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While the size of the population over the last several years remained stable, the number dropped in 2008 and 2009 and increased in the 1990s through the early 2000s. Pew said the number peaked at 12.2 million in 2007.

Since 2009, Pew said that number of people in the U.S. who are foreign-born has risen since 2009, increasing by nearly 3 million between 2009 and 2014.

This comes a few days after the Associated Press reported that an internal Homeland Security audit revealed the U.S. government mistakenly granted citizenship to at least 858 immigrants from countries of concern to national security.