The city is trending younger as the suburbs quickly grow older.
There are fewer young children in the region.
And Pennsylvania remains one of the grayest states.
Those were some of the snapshots to emerge in new census data to be released Thursday.
That the state shows signs of aging didn't surprise researchers or other officials who work daily with an older population.
"It is something we absolutely are seeing," said Wanda Stonebraker, director the Chester County Department of Aging Services, which provides meals, medical assistance, and transportation for seniors. "The phone calls are incredible; we probably get 1,000 a month."
For decades, researchers have predicted the graying of America, pointing to longer life spans and the aging of the baby boom generation. As a group, seniors are expected to double to 88 million by 2050.
How communities - and the nation - respond and adapt to that change will affect every American, shaping decisions on things like transportation planning, medical care, and consumer services.
Pennsylvania remains one of the trend leaders, the new data show.
Half of residents were 40 or older last year, according to the census. Of the 24 other states and territories with data released, only New Hampshire, Florida, Maine, and West Virginia had higher median ages. Information about the remaining states, including New Jersey, is scheduled to be released later this month.
Much attention has been focused on the aging of the population, but the figures show a trend at the other end of the life scale, at least in and around Philadelphia.
The number of children under 18 dropped across the region, reflecting a trend toward smaller families.
Still, Philadelphia showed signs of a youth movement. Its median age fell from 34.2 to 33.5 years. And for the second straight census, the city was home to fewer senior citizens.
Of more consequence than the numbers is where older folks are moving or settling. In Chester, Montgomery, and Bucks Counties, the median age increased by more than two years.
Half the residents of Bucks and Montgomery Counties were 40 or older last year. Seniors in those two counties now make up roughly 15 percent of their populations.
Chester County's senior population also rose, though not as much, and Delaware County recorded a slight dip.
The overall figures reflect a phenomenon experts call "aging in place," where couples or single parents stay in their suburban homes long after their children have grown.
The trend has stirred discussion about how communities should prepare for the challenge of responding to a growing population with particular problems and needs. It means more seniors traveling the roads, shopping in malls, and in need of home or medical services.
"There's all kind of implications with the suburban counties seeing this older population," said Mary Bell, manager of demographic and economic analysis for the Delaware Valley Regional Planning Commission.
Most regional facilities for older adults are straining to meet the increased demand for programs, said Susan Shapiro, executive director of the Wayne Senior Center.
She said centers like hers need to serve two diverse segments these days: the 60-somethings who want to be active and stay fit, and a less-agile population that's increasingly living into or beyond their 80s.
"We have to be creative," Shapiro said.
More than two-thirds of the 3,300 clients at Surrey Services for Seniors, a nonprofit organization in Chester and Delaware Counties, are 75 or older, with almost a quarter at least 85.
Over the last year, lunches have increased by 20 percent, and subsidized home care is up 63 percent from a year ago, according to Barbara Fentress, the group's president.
Fentress said more of her clients were staying in their homes, which is less expensive than moving to assisted-living facilities and which lets them remain a part of their communities.
"Surrey values the importance of all generations living in the community," she said. "It's so fundamental to the fabric of a healthy community."