It's only been since the 2000 Census that respondents were given the option to identify themselves as having more than one race, so the data do not go beyond that.
So the 2000-2010 period marks the first time demographers were able to examine the trend of multiple races with any accuracy.
"These comparisons show substantial growth in the multiple-race population, providing detailed insights to how this population has grown and diversified over the past decade," said Nicholas Jones, chief of the U.S. Census Bureau's Racial Statistics Branch.
Among the findings:
-Four groups comprised the largest multiple-race combinations, each exceeding 1 million people in size. White and black, at 1.8 million people, represented the largest combination.
It was followed by white and "some other race" (1.7 million); white and Asian (1.6 million); and, white and American Indian and Alaska Native (1.4 million).
-Since 2000, the combination of white and black population grew fastest, adding more than 1 million people, and increasing by 134 percent.
Meanwhile, the white and Asian population grew by about 750,000, and 87 percent.
-The top three states reporting people of multiple races are California, Texas and New York.
-Those showing the fastest rate of change were mostly in the South, including South Carolina, North Carolina, Delaware, Georgia, Kentucky, Tennessee, West Virginia, and Mississippi.