Katie Cristol, 32, who’s been on the Arlington County Board just two years, became chair of the board on Tuesday night. (Patricia Sullivan/The Washington Post)

A year ago, as the newly elected vice chair of the Arlington County Board, Katie Cristol (D) said she wanted to improve child-care options for the many working families in this inside-the-Beltway suburb.

On Tuesday, she became chair of the five-member board, a position that rotates annually among members of the majority party. But her day-care initiative is still in its infancy, and she describes her efforts to shepherd the project as her “initiation in government.”

Cristol, who will turn 33 later this month, was elected to the board two years ago. She takes the helm as Arlington and the rest of the region struggle with pressing mass transit needs and the looming economic threat of sustained cuts in federal spending.

In addition to child care, Metro funding and housing affordability, Cristol said she wants to emphasize regional cooperation.

“We are going to rise and fall with Fairfax and Prince William and, increasingly, other, outer jurisdictions to make a case for transit . . . and quality of life in this region collectively,” she said.

Cristol is the first millennial to lead what has become a county dominated by the young-adult demographic. Almost one-third of the county’s population in 2017 was age 20 to 34; Arlington has been ranked as the best city in the nation for millennials, with the highest population growth for that age group between 2007 and 2013.

Her board, too, is relatively inexperienced by Arlington standards. The most veteran member, Libby Garvey (D), has served since 2012, although both she and the next-most-veteran member, John Vihstadt (I), have years of experience in school and community affairs.

“I know that my age precedes me, and people form an opinion about me prior to even meeting me,” Cristol said in an interview Tuesday. “There are people excited by the idea of a generational change. There are people for whom my very presence is a worry. . . . The solution, I think, is to do the work.”

She said her time on the board of the VRE commuter rail system has shown her how interdependent and connected the region is. Liberal Arlington and more conservative Stafford County may be politically different, she said, but they “have something big” — the rail line — “in common.”

Cristol said she will put her work as an education consultant on hold this year while she guides the board, itself a $59,610-a-year job that requires many night and weekend hours.

An active campaigner last year for Virginia Democratic candidates, she did not rule out future statewide campaigns for herself but said she expects to be fully absorbed in Arlington for now.

“One of the benefits of being elected at a relatively young age is you do have what I hope will be a long future,” she said. “But I’m also cognizant that this . . . is not an entry-level job and that’s where I’ll keep my focus.”

On the child-care initiative, she credits fellow board members and others for working last year to include money in the budget for a study of how to coordinate state and local child- care regulations.

A public hearing to solicit ideas for improving child-care options in Arlington will be held Jan. 25, after which an interagency task force will work to prepare recommendations for the board.

“By the end of calendar year 2018, we’ll have been able to take some actions . . . to really start expanding supply,” Cristol said. “It will be a multiyear project.”