COLUMBIA -- Retirees accounted for the largest population gain over the last decade in South Carolina, according to census data released this week.

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Since the last national count in 2000, the number of South Carolina residents ages 55 to 74 years old jumped by about 300,000 people, about half of the state's total population increase. South Carolina's overall population has gone up by more than 610,000 people, a 15.3 percent increase, to more than 4.62 million.

That makes South Carolina the tenth-fastest-growing state in the country and the 24th most-populous.

South Carolina's median age also went up over the decade, from 34.5 years to 37.9 years.

Noting that the older population can strain already over-burdened state resources, Patrick Cobb of AARP South Carolina said older residents also contribute to their communities by volunteering and mentoring.

Many of those residents are concentrated along the state's coastline, a traditional home for South Carolina retirees.

Overall, Columbia's population was the state's largest, with 129,272 residents.

All the state's urban and suburban counties saw significant population increases overall, and particularly in the older age groups. In Charleston County, home to the state's second-most-populous city, residents ages 55 to 74 accounted for more than 19 percent of the total population in 2010, more than four percent higher than a decade ago.