There were 11.7 million immigrants from Mexico living in the U.S. in 2014, and about half of them were in the country illegally, according to Pew Research Center estimates. Mexico is the country’s largest source of immigrants, making up 28% of all U.S. immigrants.

With President Donald Trump’s administration taking steps to reduce the number of unauthorized immigrants in the U.S. — including through the construction of a wall at the southern border — here’s what we know about illegal immigration from Mexico:

1The number of Mexican immigrants living in the U.S. illegally has declined by more than 1 million since 2007. In 2014, 5.8 million unauthorized immigrants from Mexico lived in the U.S., down from a peak of 6.9 million in 2007. Despite the drop, Mexicans still make up about half of the nation’s 11.1 million unauthorized immigrants (52% in 2014).

2More non-Mexicans than Mexicans were apprehended at U.S. borders in fiscal year 2016 for the second time on record (the first was in fiscal 2014.) In fiscal 2016, 192,969 Mexicans were apprehended, a sharp drop from a peak of 1.6 million apprehensions in 2000. The decline in apprehensions reflects the decrease in the number of unauthorized Mexican immigrants coming to the U.S.

3Mexicans were deported from the U.S. 242,456 times in 2015 – up from 169,031 in 2005, but down from a recent high of 309,807 in 2013. The increase over the past decade is due in part to a 2005 shift in policy that increased the chances of being deported following apprehension in the border region. Prior to that change, many unauthorized immigrants were returned without a formal deportation order.

4Mexican unauthorized immigrants are more likely to be long-term residents of the U.S. As of 2014, 78% had lived in the U.S. for 10 years or more, while only 7% had been in the country for less than five years. By comparison, 52% of unauthorized immigrants from countries other than Mexico had lived in the U.S. for at least a decade as of 2014, while 22% had lived in the U.S. for less than five years.

5Unauthorized immigrants from Mexico make up at least 75% of the total unauthorized immigrant population in three states.This is the case in New Mexico (91%), Idaho (87%) and Arizona (81%). In California, Mexicans make up 71% of the state’s unauthorized immigrant population, and they numbered more than 1.6 million in 2014 – the highest total of any state.