The U.S. immigrant population hit a record high in 2015 and the the growth last year was led by Mexican immigrants, according to an analysis of Census Bureau data by the Center for Immigration Studies (CIS.)

The immigrant population reached 42.1 million in the second quarter of this year, an increase of 1.7 million since the same quarter of 2014. 

The growth was led by a 740,000 increase in the number of Mexican immigrants, which represents 44 percent of the increase in the total immigrant population in the last year. 

The report by CIS — an organization that advocates for lower immigration — says the “the number of immigrants in the United States is now enormous, but it must be recognized that most immigrants, including those from Latin America, are in the country legally”. 

CIS claims the report is based in monthly Census Bureau data, referred to as the Current Population Survey (CPS). However, it must be noted that the organization has been subject to criticism and even labeled as a “False-Fact Think Tank.”

According to Media Matters for America, CIS was founded in 1985 by John Tanton, an anti-immigrant nativist with ties to other anti-immigrant organizations such as NUmbersUSA and the Federation for American Immigration Reform (FAIR), which the Southern Poverty Law Center labeled as a hate group.