This story is part of a series on the changing face of Philadelphia as reflected in the new 2010 census figures.
Seeking an "urban lifestyle," Heather McKay moved into Center City four years ago even though she works in Montgomery County.
"There's so much to do" in the city, she said, as she walked her black rat terrier, Clark, around Rittenhouse Square yesterday.
She lives near the park and particularly likes the city's nightlife - hanging out at Time restaurant and bar and the Continental Midtown, especially its rooftop.
McKay, 25, moved here from Blue Bell, where she grew up, and drives to her marketing job in Plymouth Meeting.
She is one of the 50,306 young adults, ages 20 to 34, who helped contribute to the city's population growth from 2000 to 2010, according to census data being released today, which show breakdowns of residents by age groups.
Last year, there were about 393,000 people ages 20 to 34 who lived in the city, accounting for 26 percent of its residents.
While the city grew by a mere 8,456 people, or 0.6 percent, much of the increase was attributed to these young professionals who live in Center City, South Philly east of Broad, and the Manayunk and Roxborough area, according to a Daily News analysis.
Adults ages 55 to 64 also boosted the city's population, with 35,592 more of them living here, particularly in the Northeast, West Mount Airy, Germantown and Center City, based on data released along state representative-district boundaries.
But a large decrease in the city's population was that of children ages 5 to 14, a group that saw a 43,370 decrease, suggesting that families with school-age kids moved out of the city for better opportunities.
Along those lines, the number of adults aged 35 to 54 declined by about 16,000 over the decade.
The growth in young professionals shows that the city has "retained more of our graduating seniors," said David Bartelt, a professor of geography and urban studies at Temple University, adding that the city has been strong in service-sector jobs, such as tourism and the restaurant business, and in creative endeavors, such as the arts and public relations.
As for why families with younger, school-age children declined, Bartelt said it could be because of a lack of employment opportunities in traditional job sectors, making people look elsewhere, even out of this region.
Gary Jastrzab, executive director of the City Planning Commission, said some families with school-age children may have moved out so their kids could attend suburban schools.
With the rise in people ages 55 to 64, Jastrzab said the new data back up anecdotes that have said empty-nesters in their peak earning years or entering their retirement period have been moving into the city "looking for more active lifestyles" or to be close to the arts.
He also noted that Philly has been attracting young adults because of its affordable housing, active nightlife and ease of getting around by public transportation, walking or biking.
Although some professionals 35 and older have moved out of the city, Anthony M. Santaniello moved back into the city in 2001. He had lost his job in New Haven, Conn., and really missed the city.
"I was longing for the little streets, little cobblestone alleys," said Santaniello, who had also previously lived in Chicago.
Santaniello, 39 and single, who works at the City Planning Commission, bought a house five years ago east of Broad Street, near Ritner, in South Philly. He takes the subway to work and likes to walk around the city.
Merritt Lentz, 34, also loves the convenience of the city. He moved to the Rittenhouse Square area from Wynnewood in 2007 to be in walking distance to his job at a law firm here.
He also enjoys being able to take the Broad Street Line to watch Phillies games, and likes Rittenhouse Square, where he was walking his chocolate Labrador retriever, Riley.