The latest estimate by the Pew Research Center puts the number of immigrants living illegally in the U.S. at 11.7 million.

This new number, based on U.S. government data, can be found in a report released Monday titled "Population Decline of Unauthorized Immigrants Stalls, May Have Reversed." The key word in that headline is "may." As the authors write in the report:

"Although there are indications the number of unauthorized immigrants may be rising, the 2012 population estimate is the midpoint of a wide range of possible values and in a statistical sense is no different from the 2009 estimate."

And 2009 was when the estimated number of immigrants living illegally in the U.S. fell to 11.3 million, after a peak year at 12.2 million in 2007. The size of the population dropped sharply during the recession, and since the recession's official end in 2009, it has remained stalled at about 11 million.

This trend coincides with record levels of deportations under the Obama administration, which deported almost 410,000 people last year.

Jeffrey Passel, a senior demographer at Pew's Hispanic Trends Project who co-authored the report, says deportation stats indirectly impact Pew's estimate, which is mainly based on analysis of the number of foreign-born residents from Census surveys and the number of legal immigrants from the Department of Homeland Security's Office of Immigration Statistics.

But Passel adds that deportation numbers include a mix of immigrant populations, some of which are not counted in Pew's estimate.

"Some of the deportations are really people who haven't lived in the U.S," he says. "[Some of them are] people who got caught trying to enter the U.S. illegally, and they were put through deportation proceedings."

The new report also notes that while Mexico is the main source of unauthorized immigrants (at 52 percent in 2012), the estimated number of Mexican immigrants living illegally in the U.S. has been on the decline since 2007, with around 6 million in 2012.

The estimated number of unauthorized immigrants from other countries, however, appears to be on the rise since 2009.

"The total [of unauthorized immigrants not from Mexico] for 2012 (5.65 million) appears to be higher than the 2007 peak [5.25 million]," the report says, "but because of the large margin of error, this cannot be confirmed with the preliminary estimates."

The Pew Research Center plans to update its estimates when additional Census survey data are released later this year.

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