Chester grew 15.1 percent, Montgomery 6.8 percent, and Bucks 4.6 percent.
Pennsylvania's overall population increased 3.4 percent, to 12,702,379, with the bulk of the growth concentrated in the southeast.
Counties in the western and north-central parts of the state largely lost population, with Allegheny County, home to Pittsburgh, shedding 4.6 percent of its people.
Upper Uwchlan, in Chester County, grew 63.9 percent, which township manager Cary Vargo attributed to its "central location" and easy access to the "employment centers" of Philadelphia, King of Prussia, Wilmington, and Allentown. That combination helped raise its population from 6,850 in 2000 to 11,227 last year.
In part, that growth was fueled by an increase in the township's Asian population. In 2000, Asians made up 1 percent of the municipality's population, according to the census. Now numbering 1,587, they are 14 percent.
Unlike the Census Bureau's annual estimates, which are sample-size surveys that include margins of error, the decennial census, mandated by Congress, attempts a complete count of the nation's population and its racial characteristics. The head count will be used to apportion U.S. House seats and redraw statehouse districts.
Diversity has contributed to the region's growth. Although the suburbs remain overwhelmingly white, the percentage of nonwhites was up in 97 percent of the region's municipalities.
In 2000, just 10 of the cities, townships, and boroughs were majority minority. Now, with the addition of Lansdowne, East Lansdowne, and Sharon Hill in Delaware County and Kennett Square in Chester County, 14 are majority minority.
Latinos drove the increase in Kennett Square, for example, where minorities make up 57 percent of the population, but Latinos alone account for 49 percent.
At 799,874 people, Montgomery is the state's third-largest county. Bucks' population is 625,249. Delaware's is 558,979. Chester's is 498,886.
Dominic A. Pileggi, chairman of Concord's Board of Supervisors, said the sewage-treatment plant that went on line in the early 1990s was a critical boon to development a decade later. Before that, all properties used septic systems.
"Once the sewers came, the rooftops came," he said, "and everybody started moving here."
And that changed the demographics.
"We couldn't get a retailer [to move] up here to save our lives," Pileggi recalled. But after the population soared, "we started getting shopping centers, hotels, and things of that nature."
Back at Merion's Produce Hut, customer Gilda Mock, a nurse case manager, said her parents had moved from Ardmore to Concord about 50 years ago, "when there were very few people around."
Unlike many of the newcomers, she and her husband, Bill, were raised in the township.
"I enjoy the changes," said Mock, grabbing some groceries with her daughter. "But, sometimes, I wish they would have preserved a little bit more open space."
A township proposal that was overwhelmingly passed in a referendum about seven years ago earmarked about 25 percent of local taxes to acquire public land. Close to 150 acres have been purchased, Pileggi said.
At the nearby Chester Heights Post Office, postmaster John Russo said population growth in the last decade had driven a threefold increase in customers' purchasing stamps and shipping packages.
"The area has changed dramatically," he said, adding 10 minutes or more to what used to be a 30-minute commute to his home in West Grove, Chester County.
The upside, he said, is the opportunity to pick up something at Home Depot or Borders, two relatively new stores, on his way home.
John Merion said his customers were younger and more mobile now and often commuted to Wilmington, Philadelphia, and even New York City for jobs.
"I don't like to use the word affluent," he said, stroking his white mustache, "but they are building million-dollar homes."
Contact staff writer Michael Matza at 215-854-2541 or firstname.lastname@example.org.