Jace Knight had heard about Somerville, Mass., while working on a Ph.D. at the University of Alabama in 2020.

The small city had recently passed a law granting domestic partnership rights, like the ability to receive employment benefits or make hospital visits, to people in polyamorous relationships. Mx. Knight, who is nonbinary and has been nonmonogamous since 2014, was impressed.

In late March, Somerville passed two more laws extending the rights of nonmonogamous residents, this time banning discrimination on the basis of “family or relationship structure” in city employment and policing. (A similar ordinance, focused on housing, is currently being discussed by the Somerville City Council.)

Around the same time these new laws passed, Mx. Knight, 38, now with a Ph.D. in applied mathematics, moved from Alabama to a house in Somerville with their two partners and a partner of one of those partners. The city’s attitude toward nonmonogamy was a big factor in the group’s decision to move there, Mx. Knight said.

In recent years, Somerville, a four-square-mile city with 80,000 residents just outside Boston, has quietly turned into something of a haven for those who practice consensual nonmonogamy, an umbrella term for relationship styles that involve more than two people. One of these is polyamory, which involves intimate or romantic connections with multiple people and the knowledge and consent of everyone involved. Polygamy means to be married to multiple people simultaneously.

Somerville is close to Harvard University and Massachusetts Institute of Technology, and claims to have more artists per capita than any city besides New York. Often described as “hippie” or “bohemian,” the city is staunchly L.G.B.T.Q-friendly. There is a significant crossover between those who identify as lesbian, gay, bisexual, trans and pansexual and those who practice nonmonogamy, according to multiple studies.

“We’re a very queer city,” said Willie Burnley Jr., 29, a city councilor at-large who introduced the new ordinances and who is polyamorous. “We have a population that’s more open to these ideas, and many of these folks are either currently nonmonogamous or have tried nonmonogamy or at the very least know someone who’s polyamorous.”

Somerville is alive with events like Indecent, a fetish- and kink-positive party, and Boudoir, a queer underground dance party. There are polyamorous speed-dating evenings, drag shows at the venue Crystal Ballroom and a gender-neutral CrossFit gym.

Wil Hall, 30, a software engineer, has lived in Somerville for eight years and has been polyamorous for half that time.

“Over time I’ve had the recognition that more love is never a bad thing,” said Mx. Hall, who is currently dating two people, each of whom is dating another person.

Mx. Hall said, “half of the businesses on one commercial street have an inclusive symbol, like a pride flag or a Hate Has No Home Here sticker. Because the city is so small, Mx. Hall said, there’s a density of inclusive spaces that makes people like them feel safe.

In 2020, when Somerville decided to create a domestic partnership ordinance for the first time in response to the medical needs of residents during the pandemic, J.T. Scott, a city councilor, asked why the new category should be restricted to couples.

“Everyone in Somerville City Council knows someone who’s in a polyamorous or multiple-partner relationship,” he said. “It’s very common here.” Other councilors agreed and the ordinance, which allows people in multi-person relationships, including those living outside Somerville, to register as domestic partners, easily passed.

After Mr. Burnley was elected to the city council in 2021, he watched a webinar in which anti-discrimination ordinances were named as the next step for the multi-partner rights movement. “It made sense that Somerville should be the place to do that,” he said. “We were the first around the domestic partnership ordinance, and we have a leadership role to play in this movement.” Like the domestic partnership ordinance, Mr. Burnley’s anti-discrimination ordinances were approved by the city council unanimously.

“In my dream world, Somerville can be a safe haven for all walks of life, including if you’re a normie who’s very vanilla and just want to settle down, and someone who wants to have off-the wall parties on the weekends,” Mr. Burnley said.

Interest in nonmonogamy seems to be on the rise across the country, buoyed by TV shows like “Planet Sex With Cara Delevingne” and “Sex Diaries”; or discussed publicly by people like the psychologist Esther Perel and the actress Jada Pinkett Smith (on her show “Red Table Talk”).

According to some research, about one-fifth of Americans say they have been in a consensually nonmonogamous relationship at some point in their lives.Dating apps like Feeld and OkCupid have made finding like-minded people much simpler by allowing users to list nonmonogamy as a preference and to link their profiles to those of their partners.

Gabrielle Smith, 27, a writer and digital content creator in Brooklyn who focuses on nonmonogamy and relationships, said that more people trying nonmonogamy has led to more conversations about it, which has led to more people trying it — or at least thinking about it.

“It’s definitely becoming more of a movement,” Ms. Smith said. In recent years organizations focused on nonmonogamy have initiatedpolitical and legal action, aggregated resources and developed scientific research.

After Somerville passed its domestic partnership law, Arlington and Cambridge, two other cities in Massachusetts, added polyamorous units to their existing domestic partnership ordinances. But once people register as domestic partners there, benefits may extend beyond Massachusetts as well: “So people around the country are able to come get registered and go home to generally use it as they would any other domestic partnership they registered for in their home city or anywhere,” Diana Adams, executive director of Chosen Family Law Center and one of the people who helped write the anti-discrimination ordinances for Somerville, wrote in an email.

The isolation and turmoil of the coronavirus pandemic may have also played a role in some people choosing to look beyond a two-person relationship model, said Rebecca Alvarez Story, a sexologist and the chief executive of Bloomi, a company that makes sex toys and produces sex education content. With polyamory, she said, people are thinking, “I might be more fulfilled, I’ll get more help with my family, the financial burden is shared more.”

Nevertheless, people in nonmonogamous relationships are still often perceived and represented negatively. Some are afraid to come out at work for fear of being fired or overlooked for promotions, since there are no employment protections on the basis of relationship structure. Parents sometimes lose custody battles in family court because they have multiple partners.

For the most part, the Somerville ordinances will not fix these problems. The anti-discrimination ordinances are very limited in scope; and though the domestic partnership law is more broad and allows polyamorous people from outside Somerville to register as domestic partners, it will not protect someone from being fired or from having their children taken away. But supporters of the laws say there is significance in what they symbolize.

“We’re no longer operating where it’s a heteronormative, cisgender woman and man, and 2.5 kids,” Ms. Story Alvarez said.

Ryan Malone, 37, a chemist who has lived on and off in Somerville for six years, said that he knows hundreds of people who identify as polyamorous, through his extended social circles. Mr. Malone, who has been nonmonogamous since he was in college, currently has a nesting partner, a long-term partner, two long-distance partners and a kink-based relationship with another person.

Mr. Malone said he has never felt weird about going on dates with two or more people at the same time in Somerville. “No one seems to bat an eye,” he said, so he sees the new protections as very subtle.

Ashley Kirsner, 33, who has lived in Somerville for seven years, is the founder of Skip the Small Talk, an organization that offers speed-friending and speed-dating events around the country. In 2018 the group held its first polyamorous speed-dating event in Somerville.

Events like these, the support of the community and the city ordinances have helped Mx. Hall feel more seen. “Every time a new book comes out, or a new protection comes into place, it feels like it’s validating your identity,” they said.