PORTLAND — About one quarter of Lincoln County’s population was over age 65 in 2013, epitomizing a trend in which Maine leads the nation: getting older.

In 2010, the share of Lincoln County residents older than 65 was about 4 percentage points lower.

With a population that has remained flat in recent years, the pace of Maine’s aging — as revealed by new U.S. Census data released Thursday — is no surprise to economists. Generally, workers are staying on the job later in life, but the Maine Department of Labor’s chief economist, Glenn Mills, said the trend continues to raise concerns about the labor force.

“These population dynamics explain why Maine is experiencing slow growth in [gross domestic product], personal income, employment and other economic measures,” Mills said in an email to the Bangor Daily News after reviewing newly released census data Thursday. “Our workforce is barely growing, and the challenges to growth will increase in the years ahead unless we are able to entice more young people to move to the state.”

Amanda Rector, state economist at the Governor’s Office of Policy and Management, said in an email that it’s a familiar refrain.

“The latest figures just reconfirm the demographic challenges we know Maine is facing,” she saide. “The county data gives us a more detailed look at what is happening in different regions, but those are also continuations of existing trends.”

Lincoln County, with the state’s highest median age, also had the state’s most rapidly aging population. Its median age rose 3.53 percent, to 49.8, from 2010 to 2013.

The slowest county to age statistically from the 2010 census to the latest figures for 2013 was Kennebec County, where the median age rose 2.34 percent to 43.8.

Overall, Maine’s median age in 2013 was 43.9. For comparison, the national median age rose just more than 1 percent, to 37.6 years, from 2010 to 2013.

The census data released Thursday gives a more detailed look at how each age group in the state’s workforce is changing in each county. Those trends indicate to Mills that the demographic challenges the state faces aren’t going away anytime soon.

“Labor force participation declines at an accelerating rate with age after 54, and most of our population growth was among those age 55 to 74, up 32,700,” Mills said.

Six of Maine’s 16 counties saw decreases in the population of residents between age 18 and 24, and just one county — Penobscot — saw an increase in people between age 25 and 44.

Every county saw a more than 90 percent rise in the number of people between the age of 45 and 64 from the 2010 census to 2013, and growth in the number of residents age 65 and older ranged from 5.6 percent in Aroostook County to 15.1 percent in Waldo County.

The county with the smallest share of residents over the age of 65 in 2013 was Androscoggin County, at 15.5 percent. Nationally, 14.1 percent of the population was over that age in 2013.

While Maine has the highest median age in the country, none of its counties are close to the oldest county in the country. That designation belongs to Sumter County, Florida, where the median age was 65.5 last year.

The youngest county in the country was Madison County, Idaho, at 23.1.

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