Alan Gomez

USA TODAY

The number of undocumented immigrants living in the U.S. remains steady at 11.1 million for the sixth straight year, as a drop in people coming from Mexico is offset by an increase from the rest of the world, according to a report released Tuesday.

After two decades of continuous growth, the country's undocumented immigrant population peaked at 12.2 million in 2007. Once the Great Recession started in 2008, that number dropped and has remained steady since 2014, according to the report from the Pew Research Center, based on the most recent data available.

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That has changed the nature of undocumented immigrants in America, with more of them becoming long-term residents established in their communities. In 2014, 66% had lived in the U.S. for 10 years or longer, compared to just 36% in 2000.

"As the U.S. unauthorized immigrant population has stabilized, it also has become more settled," co-authors Jeffrey Passel and D'Vera Cohn wrote in the report.

The new numbers come as immigration dominates the race for the White House. Republican Donald Trump has called for building a giant wall along the southern border and for closer screening of would-be immigrants trying to enter the country. Democrat Hillary Clinton is pushing for more legal protections of undocumented immigrants living in the U.S. and expanding programs to accept refugees from abroad.

Mexicans continue to make up the largest share of the undocumented immigrant population at 52%, according to Pew. But with Mexico's economy improving and an aging population, plus fewer job prospects in the U.S. and tighter border security, fewer people are making the trek to the United States, dropping Mexico's share of the undocumented population in recent years.

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They have been replaced by people coming from sub-Saharan Africa, Asia and Central America. Over the last six years, Pew estimates the number of people illegally immigrating from Africa has increased 37.5%, the number from Asia has increased 11.5% and those from Central America have increased 6.3%.

Pew cites a variety of reasons for those increases, from raging drug violence in Central America to limited economic opportunities in Africa and Asia.

The report was based on Pew's analysis of information from the Census Bureau.