The neighborhood with the largest percentage of young adults in Philadelphia, according to data released Thursday, is Manayunk. Today, 59 percent of residents there are in their 20s or 30s, up from 43 percent in 2000.
Southwest Center City mirrored the growth in Northern Liberties. The young-adult population there grew by 65 percent, and that share of the population jumped from 35 percent to 53 percent.
"It's perfect," gushed Sandra Clark, 33, who moved to Center City four years ago, and who was out for a walk Wednesday near 16th and Pine Streets. "It's in the middle of everything."
The two neighborhoods with the highest percentage of growth in young adults also had the most growth in wealth.
Average household income in Southwest Center City rose from $42,677 in 1999 to $68,644 in the five years from 2005 to 2009 - a 61 percent increase. Income in Northern Liberties rose 57 percent, from $50,730 to $79,476, according to estimates from the Census Bureau's American Community Survey. The figures are adjusted for inflation to represent 2009 dollars.
Citywide, however, average household income from 2005 to 2009 declined 5 percent, to $51,037.
Philadelphia now has six neighborhoods where young adults constitute majorities: Manayunk, Northern Liberties, Southwest Center City, University City, Center City, and Fairmount/Spring Garden.
The section of North Philadelphia west of Broad Street near Temple University had a dramatic rise in people in their 20s - up 74 percent. They now account for 21 percent of all people living in the area, up from 12 percent in 2000.
Citywide, the increase in young people was not as dramatic. The percentage of residents in their 20s and 30s grew 7 percent between 2000 to 2010. As a percentage of the total population, younger people increased from 30 percent to 32 percent.
Center City and the ring of surrounding neighborhoods were happening places, with growth among all age groups. And many young people who don't live in Center City make it their playground.
Graham Shapiro, 25, walked out of the Apple store on Walnut Street on Wednesday, holding a bicycle helmet in one hand and a Barnes & Noble bag in the other. He lives in West Philadelphia, but Center City is where he comes for fun.
"Everything is close together, the restaurants, and it's walkable," he said.
His girlfriend, Lior Levy, 31, could instantly name her favorite Center City venue.
"Rittenhouse park," she said. "The movement of the people, the variety, the green. It's nice to have that oasis in the middle of the city."
In Center City, the population of all age groups grew 18 percent over the decade, an increase of 9,016 people. Of those, 5,175 were in their 20s and 30s.
Another long-recognized trend - the move of older, empty-nesters to Center City - is documented in the census.
Tax abatements on new condominiums, enacted in 1998, helped increase the number of residents 65 and older by 17 percent in Center City, from 7,046 to 8,250. Across Philadelphia, the opposite was true; that age group dropped 13 percent as older people left or died. Of the city's 56 neighborhoods, 44 lost seniors.
An earlier Census Bureau release showed that Philadelphia grew slightly during the last decade, adding 8,456 residents to a city now numbering 1,526,006 - but more important, halting a 50-year population decline.
The growth suggests Philadelphia's population may have stabilized after decades of drops that began when Harry S. Truman was president.
Ted Coyle, 64, has lived 30 years on Rittenhouse Square and watched Center City change.
"It's a great city," he said Wednesday as he sat in Rittenhouse Square Park. "Plenty of eateries, theater, art, a lot of nice people - and not so nice people. . . . The park attracts everyone, the richest to the poorest, every race and color. It's neat."
As he talked, a guitarist set up to play to passersby. Older people sat with their dogs, hipsters drank iced coffee with friends, and nannies pushed strollers that carried the babies of the well-off.
"It's just amazing," said former Center City resident Anita Dudzek, who was visiting the Rittenhouse area with her husband, George. "I miss the people."
They now live near Ocean City, N.J. It's nice, they say. But it's not the city.
"Any evening we didn't know what to do . . .," George began.
". . . he'd sit on the stoop, and watch Philadelphia go by," Anita finished.
Contact staff writer Jeff Gammage at 215-854-2415 or firstname.lastname@example.org.
Inquirer staff photographer Tom Gralish contributed to this article.