The trend toward an aging America—including for the country’s “oldest old” population—is continuing, according to Census data released Wednesday. Specifically, the 65+ senior population in the United States has outpaced the growth of all other age groups over the course of the last decade, and data further indicates that the oldest old age groups are expanding rapidly.

The most recent Census data finds that there were 40.3 million people who were 65 years or older as of April 2010, up 15% from 35 million a decade earlier. As of April 2010, that population represented 13% of the overall population in the United States.

The aging of the baby boom bulge is “unprecedented,” said Carrie Werner, statistician, Age and Special Populations Branch, Population Division at the U.S. Census Bureau, in a call with members of the press Wednesday.

Of older Americans, the 85- to 94-year-old age group showed the greatest increase at near 30%.

Regionally, the Census shows that the South contains the greatest number of people 65 and older, but the percentage of those who are 65+ in the Northeast is greater than in any other region. Of 21 counties that saw their 65+ populations double over the past decade, five were located in Colorado, five in Georgia and five were in Texas. Additionally, the older population is more likely to live inside a metropolitan or micropolitan statistical area.

Written by Elizabeth Ecker