Multiracial Americans have become the fastest growing demographic group.

The number of multiracial people rose 3.4 percent last year to about 5.2 million, according to the latest census estimates. First given the option in 2000, Americans who check more than one box for race on census surveys have jumped by 33 percent and now make up 5 percent of the minority population — with millions more believed to be uncounted.

Population figures as of July 2008 show that California, Texas, New York and Florida had the most multiracial people, due partly to higher numbers of second- and later-generation immigrants who are more likely to “marry out.” ….

About 1 in 13 marriages are mixed race, with the most prevalent being white-Hispanic, white-American Indian and white-Asian.