Jessica Swanson, 31, left, challenged Fairfax County Supervisor Penelope A. Gross (D-Mason). (Courtesy of Jessica Swanson (l), Photo by Dayna Smith (right))

Longtime Fairfax County Superviser Penelope A. Gross (D-Mason) fought off a spirited challenger in Tuesday’s Democratic primary, while county school board member Dan Storck beat out three other candidates for the nomination to succeed retiring Supervisor Gerald L. Hyland (D-Mount Vernon).

With all results in, Gross, 71, secured 56 percent of the 5,095 votes cast, according to unofficial results. Her challenger, Jessica Swanson, 31, got 44 percent.

Gross, who is running for a sixth term, raised more than twice as much money overall for the campaign as Swanson, a D.C. public schools administrator.

But in the last quarter, Swanson outraised Gross nearly four to one, mostly due to a large donation from Leadership for Educational Equity, a Washington-based nonprofit organization that helps teachers and other educators run for public office.

She used the money to hammer Gross for her support of a redevelopment plan in the Seven Corners area of the district that local residents worry will create too much housing density and traffic while displacing low-income immigrants.

Mount Vernon nominee Dan Storck (Courtesy of Dan Storck )

Swanson also criticized Gross for supporting county budgets that fell short of what Fairfax school officials say they need to meet growing demands in the school system of 187,000 students.

Gross characterized Swanson as a political neophyte who represented outsider interests more than local community concerns. She also trumpeted her success in bringing three new schools to the district during her 19 years in office.

Gross’s victory was closer than she initially expected.

“I’m trying to take a deep breath,” she said after the results were in. “I’m thrilled to win. I think we proved that the high-road campaign that I always try to run carried the day and people in the Mason District realized they have a good supervisor with a lot of experience who told the truth.”

Gross will face independent Mollie Loefler, 45, in the November general election.

In the Mount Vernon district, Storck, 61, won 44 percent of the 5,698 votes cast, according to unofficial results. His closest competitor, county planning commissioner Tim Sargeant, grabbed 40 percent of the vote.

Storck focused his campaign on bringing new development to the district’s busy Route 1 corridor, alleviating traffic along that thoroughfare and creating more workforce housing in the district.

He said he believes his call for more support for Fairfax schools resonated with the district’s voters.

“I think people recognize our schools are in need of better support,” he said, vowing to push for more funding from the county if he wins in the November general election. “When you’re funding schools at 2008 levels and your kids who are coming in are needier than ever before and the state continues to raise your standards, something has got to give. I don’t see how we have an alternative.”

Sargeant and the other losing candidates — county human service council member Jack Dobbyn and local business owner Candice Bennett — focused on similar themes in the district that includes the Fort Belvoir military complex and stretches from Mount Vernon south into Lorton.

Storck will face Republican nominee Jane Gandee in the November general election.