Clad in Spandex, her hair pulled back in a ponytail, and still sweaty from her exercise class, Missy Turner collected her two most important possessions: her sons, ages 1 and 3.

While Turner cooled down from her workout Wednesday, the trio lingered in the lobby of the mega-complex that has become one of the region's hottest fitness venues - the Haverford Area YMCA. "It's so new and state-of-the-art," said Turner, who lives in Drexel Hill and joined in January.

Free child care, plus the classes, an indoor track, and three swimming pools are among the amenities that have helped make the Haverford Y into what one organization official describes as the fastest-growing YMCA in the country.

With more than 20,500 members, it has become so popular that as cars pull into the expansive parking lot, attendants with flags direct them to the few available spaces - à la the Wells Fargo Center and Citizens Bank Park during games.

Since it opened in October, the Haverford Y's membership numbers have far exceeded expectations and surpassed those of Philadelphia Freedom Valley YMCA's 16 other branches. Every day, about 2,500 people exercise at the shiny building on Eagle Road.

"We couldn't be happier," said Haverford Township Commissioner Mario Olivia. "And our residents couldn't be happier with the services."

The unprecedented growth - YMCA officials set a goal of 15,000 members in the first year - is due in large measure to the location and demographics of Haverford Township, a populous Delaware County community.

It is also a manifestation of a national trend, as YMCAs expand into suburban areas where amenities such as child care, group fitness classes, and waterslides are drawing crowds.

Tremendously successful branches also benefit less profitable locations, and allow the YMCA to fulfill its mission of offering programs to all residents, regardless of their ability to pay, Y officials say.

"So some YMCAs, we acknowledge, will cost more money to operate than they bring in as revenue," said John Flynn, president of the Philadelphia Freedom Valley YMCA. "And we subsidize those in our business."

YMCAs across the country have been expanding outside major cities for the last 15 years, said Janet Kafkas, a director of strategy and organizational development for the YMCA of the USA.

"In lots of places it's been a very intentional strategy . . . to give the community the Y experience, but also to generate resources that allow us to meet needs in other areas as well," Kafkas said.

Kafkas visited the Haverford branch in December.

"They've created something that people want to be a part of," she said.

As Turner stood in the gleaming lobby midmorning Wednesday, most of the nearly two dozen treadmills were occupied in the so-called Wellness Center, a fitness room with two-story windows facing Eagle Road. In a warm, crowded pool across the complex, seniors practiced water aerobics in one corner while young children learned to float in the other.

On the second floor, joggers and walkers circled an indoor track that offered a view of the fitness center. Classrooms inside the track offered cycling and yoga classes, both crowded with what appeared to be mothers, as well as other participants of all ages.

Only the gym, where the faint smell of new paint seemed to linger, was nearly empty, with a few young men shooting hoops.

Nationwide, 840 YMCA associations operate about 2,500 branches. The Philadelphia Freedom Valley YMCA has 17 branches in five counties, serving areas from South Philadelphia to Berks County. The result of a 2012 merger of the Freedom Valley YMCA and the YMCA of Philadelphia and Vicinity, the organization is among the 15 largest YMCAs in the country by operating budget.

The $23 million Haverford Area YMCA, on the site of an abandoned bubble-gum factory, is the newest branch in Philadelphia's suburbs. Montgomery County has two similarly successful facilities; the Ambler Area YMCA, which opened in 2011, and the Spring Valley YMCA, in Limerick Township, in 2006. Those branches and the Rocky Run YMCA in Middletown Township, Delaware County, each have about 20,000 members, Flynn said.

When the Rocky Run Y opened on West Baltimore Pike in 2000, it was the region's first new YMCA in 20 years. Since then, the organization has been in a nearly constant state of expansion outside the city.

Together, the branches support one another. Flynn, who declined to say how much the new Haverford Area YMCA has earned in its first six months, said the branch was "way ahead" financially. Its extra revenue will serve the organization as a whole.

Several of the 17 branches receive subsidies from the organization's overall budget to meet their operational costs, Flynn said.

"We're serving a lot of people in those YMCAs and they're doing excellent work," he said.

The Philadelphia Freedom Valley YMCA had nearly $67 million in revenue in 2013, according to its unaudited annual report, and spent nearly $65 million. Nearly half its revenue comes from membership dues.

The Haverford branch has more than 8,000 family memberships. At $101 per month, those family membership dues alone would bring nearly $5 million to the YMCA in six months.

Single adults pay $62 per month, with lower rates for teens and seniors. The branch has given members about $250,000 in financial assistance.

Haverford likely has "the fastest-growing YMCA in the country," Flynn said.

"When you go from zero members to 20,000 members in six months I can confidently say that nobody else did that in the same six months," he said.

The YMCA of the USA does not track growth of Y branches, but Haverford is "really impressive," spokesman Kevin Dietz said.

When the new building replaced the former Main Line Y in Ardmore last fall, 3,500 members transferred to Haverford. Larry Feinberg, a board member of the Main Line YMCA during the 1990s, said the board had talked about a Haverford location for years, because "there's so many families in a 10-mile radius."

Concerns about traffic and congestion in already busy areas have thwarted other YMCA construction plans; local governments rejected proposals in Montgomery County's Lower Providence and West Norriton Townships in the last two years.

The YMCA still wants a new branch in that area, Flynn said, and the search for a site has expanded into King of Prussia and Conshohocken. Another multimillion-dollar building is under construction in Upper Hanover, Montgomery County, for the Upper Perkiomen Valley YMCA.

YMCA expansion outside the city likely will not end with those sites, especially given the recent success in Haverford.

"There's a lot of people in the suburbs and there aren't a lot of YMCAs and those kinds of services, so when we bring them there, the citizens embrace it," Flynn said. "It's just not always easy to pull off."