Democrat Erik Gutshall won a seat Tuesday night on the Arlington County Board. (Katherine Frey/The Washington Post)

Arlington County elected Democrats Erik Gutshall to the County Board and Monique O’Grady to the School Board Tuesday, continuing their party’s decades-long dominance in this wealthy, urbanized suburb.

Complete unofficial returns showed Gutshall decisively beating independents Audrey Clement and Charles McCullough with almost 63 percent of the vote.

O’Grady, a parent activist and first-time candidate, triumphed over Alison Dough and Mike Webb with almost 71 percent of the vote.

“I’m certainly very pleased with the results,” Gutshall said from a victory party, and credited his opponents for running “substantive” campaigns. “Whenever that many people put their faith in you, you have to be humbled. Even today, talking to voters at the polls, making sure Arlington remains affordable to the middle class is on everyone’s mind.”

Elsewhere in Northern Virginia, three school districts — in Fairfax County, Falls Church and Loudoun County — sought voter approval for a total of $515 million for construction or renovation, which officials said is necessary to ease overcrowding and replace aging infrastructure.

In Arlington, Democrats hold almost all levers of power. The voters there are so solidly blue that they are among the Northern Virginians who usually provide the margin of victory for Democrats who win statewide .

The five seats on the Arlington County Board are elected countywide. The four-year terms are staggered, so there is a County Board race in Arlington every year.

Gutshall was the consensus leader in the Arlington County Board race after he beat three others for the party’s nomination in the spring. A familiar name to Arlingtonians, he is chair of the local planning commission and had previously run for County Board, losing a 2016 primary battle to incumbent Libby Garvey (D).

He was endorsed by outgoing board chair Jay Fisette (D), whose departure after 20 years on the board created the open seat.

During the campaign, Gutshall focused on housing for the “missing middle” and advocated updated zoning laws that he said will allow more creative development. He also pushed for more transparency in local government.

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Clement had lost five previous county board races since 2011 (she also ran unsuccessfully for School Board in 2014). She campaigned this year on her effort to break the local Democratic Party’s dominance.

Once a nominee of the Green Party, she ran during the past several elections as an independent who is critical of the county’s practice of distributing surplus budget money into favored projects without going through the rigor of a normal budget process. Clement, a federal IT contractor, once unsuccessfully pushed a referendum to create a public housing authority in the county.

McCullough, an attorney who was a student member of the Montgomery County Board of Education in the mid-1990s, has lived in Arlington for the past 10 years and described himself as “an independent progressive” who believes developers are not charged enough to cover their impact on the community.

Rather than spending millions to attract major employers such as Nestle, he said, the county should use its resources to help small existing businesses. Metro, whose Arlington stations draw about 50,000 customers on an average weekday, should only get dedicated funding if it meets stringent safety standards, McCullough said.

In the School Board race, three newcomers faced off for one of the five-member board’s four-year terms. O’Grady beat incumbent James Lander (D) in the spring party caucus, capturing the Democratic nomination.

A broadcast journalist who later turned to public relations, she worked on a multitude of school committees and led the effort to pass a $138.8 million school bond in 2016.

Dough said her priorities were inclusion of special-needs children into general education settings, more and longer recesses, year-round schools and more foreign-language immersion programs.

Webb, who ran for Congress in 2016 — first as a Republican and then, when he did not get the nomination, as an independent — said he would push to close the achievement gaps in Arlington schools by introducing more charter schools.

A former Army officer, he said he is sharply opposed to renaming Washington-Lee High School, an idea raised by some parents in August after a clash between white supremacists and counterprotesters turned violent in Charlottesville.