show an estimated 870,000 Mexican nationals left Mexico to return to the U.S. It is hard to track of this because there is no official number of immigrants going to the United States or returning to Mexico every year. Characteristics Since about 2014, most undocumented immigrants living in the U.S. have been long-term residents. In 2014, about two-thirds (66%) had been in the U.S. for ten years or more, while just 14% had been in the U.S. for less than five years. Just as the total population of undocumented immigrants in the U.S. has declined since 2007, the proportion of undocumented immigrants in the workforce has also declined; in 2012, illegal immigrants made up 5.1% of the U.S.'s civilian labor force. Unauthorized immigrant workers are over-represented in certain economic sectors, making up 26% of farming, fisheries, and forest workers; 17% of cleaning, maintenance, and groundskeeping workers; 14% of construction workers; and 11% of food preparation workers. Origins As of 2017, the majority of undocumented immigrants are not Mexicans, with the percentage of illegal immigrants that are Mexican steadily declining over recent years. The number of Mexican documented and undocumented immigrants in the United States grew quite rapidly over the 35 years between 1970 and 2004; increasing almost 15-fold from about 760,000 in the 1970 Census to more than 11 million in 2004—an average annual growth rate of more than 8 percent, maintained over more than three decades. On average the net Mexican population, both documented and undocumented, living in the United States has grown by about 500,000 per year from 1995 to 2005 with 80 to 85 percent of the growth attributed to unauthorized immigration. There was a net gain of 2,270,000 Mexican immigrants to the US between 1995 and 2000; a net loss of about 20,000 between 2005 and 2010; and a net loss of 140,000 between 2009 and 2014. The total number of Mexicans residing in the US, with and without authorization, was 11.7 million in 2014, down from the peak of 12.8 million in 2007. The drop is primarily the result of the decrease in the number of unauthorized migrants—which make up 48% of the Mexican population in the US in 2014, down from 54% in 2007. 2014 status Out of the entire workforce in the United States, 8 million were undocumented immigrants. This number includes immigrants who either found work illegally or are working in people's