 In fact, it has been estimated that 37% of all Mexican immigrants to the United States in the 20th century arrived during the 1990s.In 2000 approximately 20 million American residents identified themselves as either Mexican, Mexican-Americans or of Mexican origin, making "Mexican" the sixth-most cited ancestry of all US residents.In 2000 the INEGI estimated that about eight million Mexican-born people, which then was equivalent to 8.7% of the population of Mexico itself, lived in the United States of America.