The Mexican migration has been one of the largest in the nation’s history. About 12 million Mexicans have crossed the border, more than half illegally. That flow not only stopped but may have actually have begun to reverse, an equally historic shift. The report found that from 2005 to 2010, “about 1.4 million Mexicans immigrated to the United States and about 1.4 million Mexican immigrants and their U.S.-born children moved from the United States to Mexico.” The drop is the first of any significance in more than two decades. There are 40 million immigrants in the U.S. today. Mexicans account for 58 percent of the illegal population and 30 percent of all U.S. immigrants. China is the next largest country of origin, but accounts for only 5 percent of the total number of immigrants.