Diane Blust spreads fresh soil around the perimeter of her house on April 2 in Harpers Ferry, W.Va. Blust lived in Reston, Va., for 37 years before moving to Harpers Ferry to start her permaculture and sustainable living homestead. (Ricky Carioti/The Washington Post)

An earlier version of this story incorrectly stated that the region's population grew by 62,000 residents in 2011 and 18,000 residents in 2014. Those figures were net migration totals, and not for overall population. The story has been corrected.

After decades of expansion, new census numbers show that population growth in the Washington region has slowed dramatically, with Fairfax County, Arlington County and Alexandria seeing more people move out of those communities than move in over the past year.

The numbers offer stark evidence that a region defined for much of the last half-century for its affluence and growth is entering a different phase, when federal spending cuts are slowing job gains and declining suburbs are presenting new challenges for local leaders — even as pockets of extreme wealth continue to boom.

The portrait is emerging at a time when the nation is recovering from a deep recession that the Washington region largely avoided.

“Especially for young people, this may be the tip of the iceberg,” said William H. Frey, a senior fellow at the Brookings Institution. “If the broader picture is that there are more jobs in a place like Atlanta or Charlotte, then maybe some of that is pulling people away from D.C.”

The new census estimates show a dramatic trend in “out­migration” last year, with the number of people moving away on the rise — and the number moving in going down.

Population growth has slowed across the Washington region.

Even in the District, a city of about 650,000 residents where condos are popping up across the skyline and newly fashionable neighborhoods are quickly becoming unaffordable for longtime residents, net migration went down last year — from about 10,000 in 2013 to half that.

The region is still growing — thanks predominantly to births — but the growth rate continued to fall last year, as it has been doing since 2011.

That year, a region of 6 million people added about 94,798 residents (including births), according to census data. In 2014, the number of new residents dropped to 66,561.

Consider Fairfax

There is no better place to illustrate the trend than Fairfax County, Northern Virginia’s economic juggernaut and home to 1.1 million residents. Its rapid growth since the mid-20th century redefined the region, symbolized the rise of suburbs and precipitated a storied shift in economic and political strength.

Now, Fairfax is also known as the epicenter of “sequestration” — the federal budget cuts of 2013 that eliminated, according to a George Mason University analysis, 10,800 federal jobs (a 3 percent decline) and many hundreds more among federal contractors. Last year, federal spending in the region was $11 billion lower than 2010 — a 14 percent decline — according to the analysis.

All of which helps explains how Virginia’s largest county has edged closer and closer to an outright population decline.

Last year, about 7,500 more people left Fairfax than the number who arrived — the first time that has happened in recent memory, estimates show. The population grew by just 3,100 people, compared with 18,900 in 2011.

Except for a slight dip in 2006, Fairfax hasn’t seen its population veer downward since at least 1930, census figures show.

Signs of loss are sprinkled across this county of nearly 400 square miles, even as vibrant areas such as Tysons Corner and the Mosaic District in central Fairfax continue to boom.

In some commercial areas, notices for available office space hang from buildings that were once full — underscoring an office vacancy rate of about 15 percent that is the county's highest since the early 1990s.

In older communities such as Springfield and Annandale, for-sale signs stand in front of brick ramblers on blocks that in previous years were teeming with children. Web sites such as Craigslist offer an array of “moving out” sales on furniture and clothes from people planning their exit.

Steven and Natalia Potter embody some of the shift.

The couple moved to Lorton from San Diego in 2008, when the recession was underway and a subsequent surge of federal spending created jobs in the Washington area that drew thousands of newcomers from across the country.

“For my particular background and skill set, this is like the center of the universe,” said Steven Potter, 39, a former Navy SEAL who runs a company for wounded veterans that contracts with government agencies.

As time went by, that advantage was overshadowed by frustrations with traffic and the area’s high cost of living, the couple said. They plan to move to Charleston, S.C., at the end of the month, where Natalia Potter, 38, found work as an accountant. Charleston is also closer to some of her husband’s clients.

“If you’re not making more than $100,000, you can’t live the way you want to here,” she said, taking a break from moving preparations while her mother tended to the couple’s two preschool-age children inside their rented townhouse. “It’s so hectic in this area, and child care is so expensive. We don’t want to raise our kids here.”

Diane Blust, 63, echoed that sentiment. After 37 years in Reston, she moved to West Virginia last summer out of frustration with increasing density and the headaches, including traffic, that it brings.

“There’s got to be a balance,” she said, “and I just didn’t see the balance. It was pretty much all, ‘Let’s develop.’ ”

Expected development

Local and regional officials say that they’ve been anticipating a slowdown in population growth for several years.

The recent federal sequestration cuts showed how dependent the region is on government spending, so local officials are working to attract different industries, such as cybersecurity or personalized medicine, said Paul DesJardin, director of community planning and services at the Metropolitan Washington Council of Governments.

“We’re all having conversations on what we should be doing strategically to ensure the growth that we believe is likely to occur and how we can encourage it,” DesJardin said.

Like other inner-ring suburbs, the county no longer has vast tracts of land available that, during the mid-to-late 20th century, allowed Fairfax to grow by leaps and bounds — adding nearly a quarter-million people each decade.

Today, most new residential development is concentrated in former commercial or industrial areas, such as Tysons Corner and Merrifield, and it carries a distinctly urban feel.

The county is banking on these areas becoming magnets for new growth, predicting that young professionals and baby boomers wanting to live near Metrorail's Silver Line will lead to a fivefold population increase in Tysons, to 100,000 residents, by 2040.

"At the end of the day, the classic rule in real estate is location," said Aaron Georgelas, who has overseen new developments in Tysons for the Georgelas Group and based his optimism about that area on reports showing that homes near mass transit are increasingly popular nationwide.

“If we do have a population contraction, location becomes that much more important,” Georgelas said.

Officials in Fairfax and the other affected areas dismissed the possibility of a population decline, some of them pointing as an example to the fact that the Fairfax school population of 188,000 students is still growing.

“I think what we’re seeing is a leveling-off of our population from the days of our very rapid growth,” said Sharon Bulova (D), chairman of the Fairfax County Board of Supervisors.

But there are signs of a looming shift in the schools, too; officials anticipate that demographic trends will lead to a steady drop over the next decade in the number of children younger than 5.

That may alter school planning, park services and summer camps, officials said.

“It’s certainly on our radar,” said Steven H. Lewis, business manager in the county’s park services division. “There may be an impact on the horizon, we just haven’t experienced it yet.”

Craig Lilly, a real estate agent in Vienna and McLean, considered the increase in listings of homes for sale he’s seen in recent years and wondered about a shift.

“What is it that has fundamentally changed that we’re not drawing the population we used to?” he said.

Barry H. Biggar, president of the Visit Fairfax tourism group, said a population decline would affect his industry.

“Many people visit a destination to see friends and relatives,” he said. “So, depending on the decline in population, it could certainly have an impact to some degree.”

In some corners of the county, an emptiness has crept in.

Inside a three-story office building in Vienna, bank employees on the structure’s only occupied floor said they worry about vagrants, who have walked in and headed upstairs toward the vacant space.

Mary Vart, a teller, estimated that the upstairs offices have been empty for nearly two years.

“We told the owner about that,” she said, “and he finally locked the elevator and staircase.”