For Marjie Versagli, owner of Malvern Flowers & Gifts, this used to be peak season - prom corsages, Mother's Day bouquets.

But that's changed. Now, she's busier year-round.

About 20 miles away, the Lower Merion School District is in a building frenzy, adding a dozen classrooms and repurposing gymnasiums and other spaces to accommodate its largest enrollment increase in nearly 40 years.

The blooming flower business and the Lower Merion crowding are symptomatic of the region's shifting demographics. Versagli says she hasn't given much thought to the reasons behind her prosperity, "but it's all good, I know that."

While fresh U.S. census figures show Philadelphia gaining population in the last few years, experts say that appears to be largely the result of births, immigrants, and a slowdown in departures.

But the city's neighbors to the west have undergone more significant growth in that time, and that, analysts say, appears to be the by-product of an economic boomlet.

Driven by development along the Route 202 corridor, Chester County has been the fastest-growing in the region, with about an 18 percent increase in population from 2000 to 2014 - higher than any county in all of New Jersey, including Gloucester, No. 2 in the Philadelphia region at 14 percent. Montgomery County was third.

Roads, schools, and open space all have felt the growing pains - and some community frictions have flared.

Route 202 was never built to handle such a volume of traffic, so the Pennsylvania Department of Transportation has undertaken an extensive widening project that at times has been a royal pain to commuters.

But the growth has been a boon to businesses, and vice versa.

"We've got professional services, strong universities, and health-care institutions with scale in the counties," said Steve Wray, executive director of the Economy League of Greater Philadelphia. "And there's a population base that is fueling retail, among other things."

Overall, even with more tepid growth in Delaware and Bucks Counties, the five-county Philadelphia region was responsible for 84 percent of Pennsylvania's population growth between 2010 and 2014, said Wray.

Experts, demographers, and county planners say the fact that the growth has been centered in Chester and Montgomery Counties is no fluke: Both are among the most affluent in the state, with low unemployment rates and plenty of job openings.

"We've been a popular destination for people to come for a long time," said Jake Michael, a senior demographer with the Chester County Planning Commission. "We had a very big boom period in the 1980s and 1990s. We're still attracting residents."

In Montgomery County, residents have been flocking to municipalities that have development projects in the pipeline, including Limerick and New Hanover Townships, said Brian O'Leary, section chief of county planning with the Montgomery County Planning Commission.

O'Leary said the influx of residents has made streets more congested: In the last 20 years, the round-trip commuting time in Montgomery County increased nearly 10 minutes, to 54.8.

Chester County officials say some of their initiatives have been effective, including the creation of the Community Revitalization Program in 2001 to attract residents and businesses to the county's 15 boroughs and the city of Coatesville. The county has distributed more than $50 million in county and federal funds to the 16 towns since 2002.

Many of them "are really taking advantage of that to shore up their infrastructure and set the stage for development," said Patrick Bokovitz, director of the county's department of community development.

Malvern was the fastest-growing municipality in the region from 2010 to 2013, according to census figures. The 1.3-square-mile borough grew about 14 percent.

The development that comes with the growth, particularly the construction of two apartment and retail buildings on East King Street, has been a source of tension among borough residents who welcome the changes and those who worry about traffic congestion and the loss of a small-town feel.

"We've always tried to encourage municipalities to direct growth to areas that can accommodate it," said John Theilacker of the Brandywine Conservancy. "Growth is good for the county, as long as it's balanced with environmental preservation."

The conservancy is concerned about the potential strain on watersheds, and the county has developed a 10-year economic plan advocating a balance between preservation and development.

In the shorter term, Versagli finds herself at the epicenter of the county's growth, and it has had an immediate impact on her.

She's had to hire another full-time floral designer to keep up with the business.

mbond@philly.com

610-313-8207 @MichaelleBond