(from CNN)

The number of interracial couples in the United States has reached an all-time high, with one in every 10 American opposite-sex married couples saying they're of mixed races, according to the most recent Census data released Wednesday.

In 2000, that figure was about 7%.

The rate of interracial partnerships also is much higher among the unmarried, the 2010 Census showed.

About 18% of opposite-sex unmarried couples and 21% of same-sex unmarried partners identify themselves as interracial.

The term interracial, as it pertains to the study, is defined as members of a couple identifying as of different races or ethnicities.

Analysts suggest the new figures could reflect U.S. population shifts, broader social acceptance of such unions and a more widespread willingness among those polled to be classified as mixed race.

"Identifying as an interracial couple shifts over time," census spokeswoman Rose Kreider said.

Among interracial opposite-sex married couples, non-Hispanics and Hispanics are by far the most frequent combination, making up about 45% of such partnerships, Kreider said.

The second most represented group are those in which at least one person identifies as multiracial, while the third are marriages between whites and Asians.

Marriages between blacks and whites are the fourth most frequent group among married opposite-sex interracial couples.