How many Mexicans have immigrated to the United States during the 1900s?

From 1900 to 1990 about 3.5 million Mexicans immigrated legally to the United States.

Many more are believed to have come illegally. Because unemployment and destitution are perennial problems in Mexico, it is expected that Mexicans will continue to immigrate in large numbers.

Some Mexicans migrate back and forth between the two countries, going wherever jobs or family ties might lead them.