It’s a classic lesson in why every vote matters: the Boston City Council recount to determine who wins the fourth at-large seat came down to one vote.

With that single vote, Julia Mejia edged past her closest contender, Alejandra St. Guillen. The Dominican-born, Dorchester-raised progressive is poised to become the first Latina to serve on the council.

“It feels incredibly overwhelming to win by one vote," Mejia told reporters Monday night. "It really goes to reinforce the message we’ve been promoting all along, that every vote matters.”

Boston Election Commissioner Eneida Tavares announced the results at 6 p.m. Monday, three days after the recount began in City Hall. Mejia earned 22,492 votes, while St. Guillen earned 22,491.

But the matter might not settled. The St. Guillen campaign has 24 hours to decide whether it will contest the results in court, and the campaign is deciding whether to take that step.

“We believe that there are ballots that, if contested in court, would put Alejandra St. Guillen in the lead, and we’re making a decision on a formal court challenge tomorrow,” said Alec Loftus, a campaign spokesman.

When asked about the possibility of a recount, Mejia said the campaign will prepare for another review of the votes.

“At the end of the day, for me, it’s always been about building political power in low-income communities,” she said. “The more opportunities that we have to demonstrate the value of our vote, the better this story is going to be. So if we’re going to court, we’re going to court.”

In Boston, voters were instructed to back up to four candidates to fill the four at-large seats. Under state statute, the ballots with five or more votes should be discounted, said Gerry McDonough, St. Guillen’s attorney. He also worked on the 2000 U.S. presidential election recount requested by Democratic candidate Al Gore.

The Board of Election Commissioners decided how to treat those ballots on a case-by-case basis. Some were discounted, while others were included because of concerns of voter disenfranchisement, election officials said.

Born in the Dominican Republic, Mejia came to the U.S. at age five and grew up in Dorchester. She recalls working at a young age to help her mother, who at the time was undocumented.

Mejia is the founder of the Collaborative Parent Leadership Action Network, an education advocacy group. She juggled running the nonprofit with her city council campaign.

St. Guillen, a Mission Hill native, worked as a public school teacher and an education advocate. She served as director of the Office of Immigrant Advancement until earlier this year when stepping down to focus on her campaign.

St. Guillen, who has a wife and child, ran as an openly gay woman and pushed back against criticism during the campaign.

“I was asked a number of times to tone down my gayness in a few circles, and I didn’t do that,” she said.

Both candidates are progressive, Boston-bred Latinas who campaigned in communities of color. Mejia said throughout the campaign one of her biggest accomplishments was recruiting first-time voters to come out and cast their ballots.

In the Nov. 5 election, Mejia got 10 votes more than St. Guillen, coming in fourth behind incumbents Michelle Wu, Michael Flaherty and Anissa George.

St. Guillen’s campaign requested a recount after seeing how small the margin was. Once all the provisional and overseas absentee ballots were processed, they were eight votes apart.

For three days, 20 teams of counters and observers reviewed the ballots by hand.

“For the candidate, obviously it’s hard because you’re ready to be done on Nov. 5, but it also really demonstrates the good nature of good people,” St. Guillen told MassLive on Saturday. “Above everything else, I just feel this incredible amount of gratitude for everyone who stepped up.”

Before announced the results, the commissioners voted to approve one ballot and throw out another. The ballot that was approved belonged to someone who had moved within the city and voted at the wrong precinct. The second belonged to someone who wasn’t an active voter and had moved to Brookline. Commissioners didn’t say which candidates those voters backed.