The number of homeless families in the Washington region rose nearly 10 percent during the economic downturn, according to data released Wednesday as part of the Metropolitan Washington Council of Governments’ annual survey of the homeless.

One snowy night in January, surveyors went out to parks, campsites, shelters and winter hypothermia rooms for their annual “point-in-time” survey, finding 11,988 homeless people, up from 11,774 last year. Nearly a third were children and 5,315 were in families, an increase from 4,995 last year.

The number of homeless families in the Washington area has risen 9.5 percent since 2007, the survey showed. Local officials said that increase was a measure of how stressed low-income residents have become in the recession, as thousands have lost their jobs, or their homes to foreclosure.

“The poor economic conditions, coupled with the lack of affordable housing in the region, is driving more families into homelessness,” said Michael Ferrell, executive director of the District’s Coalition for the Homeless.

Lissette Bishins, executive director of the Carpenter’s Shelter in Alexandria, said that the shelter — which has 11 rooms for families — has been full since November.

“I’ve got every single bed full, and we’re seeing more and more families,” Bishins said. “The economy is coming back, but we don’t see it in our population.”

Alexandria was one of four jurisdictions where homelessness increased last year — by 16 percent. The increase was 38 percent in Prince William County, 2 percent in Prince George’s County and 6 percent in Montgomery County. The numbers held steady in Fairfax County and the District and fell in Arlington, Frederick and Loudoun counties.

The population of single homeless people showed an improvement over last year — surveyors tallied 6,673, down from 6,779.

Ferrell attributed the decrease to an infusion of federal stimulus money that targeted prevention and housing. In Fairfax, the overall number of homeless held steady — largely because of help from $2.4 million in federal stimulus funds, said Bill Macmillan, a management analyst in the county’s office to prevent and end homelessness. The county may continue funding about half of that amount in its next budget, Macmillan said, but the one-time federal stimulus funds will be missed.

Ferrell said that the loss of the federal funding is a “major concern” among housing advocates and that the totals could rise next year without it.