At the Boston Marathon, non-binary runners finally had their day. It meant the world.

“I don’t think running is here,” Riordan said, tapping their legs, then their head. “I think running is here, what space you’re in, whether or not you can push yourself to get to the next mile and the next marker and the next water station and just the next stop. And if you keep doing that for 26.2 miles, it’s done before you know it.”

A few days later, on Sunday, Riordan met up with a few other entrants for a pre-marathon shakeout run in nearby Copley Square, folks of different backgrounds and persuasions, but with one thing in common: They were among the 27 runners who registered for Monday’s race in the non-binary category, and were 24 hours away from making history.

Riordan moonlights as a standup comedian, and often opens with a bit clarifying that they’re trans and non-binary — assigned female at birth but long since removed from the use of their birth name or pronouns. They/he are preferred, with they and them doing much of the heavy lifting but he and him having their place.

“I have the non-binary marker because I have not physically transitioned,” Riordan said. “And having that, there’s just kind of an easier way to explain what I am.

“I use the pronouns they and he, and I think the closer I am to someone, the more likely they are to use he pronouns, which makes me very happy.”

Running has always been in Riordan’s life, from high school cross-country to training for their first marathon in the 105-degree Mexican heat in 2017, while they were forgoing college to work on yachts with their sister MaryKate, semi-inspired by the Bravo series “Below Deck.”

That sort of thing is par for the course for the Riordans, whose collective “why not?” approach has seen siblings Danny and MaryKate and father John run their fair share of marathons and ultra-marathons. Eldest sister Sara recently graduated from Penn State Law, and mother Tracy was a competitive swimmer once upon a time.

When MaryKate and brother Michael were signed up to run the Disney Half Marathon a few years back and the race was washed out by torrential thunderstorms, they were offered free park tickets or entry into the following day’s full marathon. They shrugged, and geared up for 26.2.

“I definitely think it’s a shared mind-set that we have,” MaryKate said with a laugh. She was the one that first traveled to South Africa to take on the 56-mile Comrades Marathon in 2019; Danny didn’t need any convincing to join a year later.

And for the most part, race registration always had a minor mental hiccup, a deep breath and a hard swallow, when the gender box presented only two options: male or female.

For non-binary or gender-nonconforming people, it’s more than a box on a screen; it’s a lack of recognition of their identity, an all-too familiar slight. Riordan had run in only a non-binary division once before this week, at the Chesterfield Gorge Ultra out in Western Massachusetts.

That was until the Boston Athletic Association announced last September that its showpiece race was evolving, including a non-binary division for the first time, for runners that didn’t necessarily identify as male or female, falling in line with other major marathons like Chicago and New York.

At a time when trans issues are in the spotlight, and legislation affecting trans and gender-nonconforming people continues to emerge, it’s a major step.

“We have the Boston Marathon, the oldest marathon in the world, and one of the Abbott World Majors,” Riordan said. “The top people come here, Eliud Kipchoge’s here, anyone who’s anyone is here.

“We have an organization this big saying non-binary people exist. The gender binary isn’t as rock-solid as you all want to think it is. These people exist, and they deserve to be able to compete on their own terms of their own gender.

“That is a very powerful statement. And it’s validating to say that this sports behemoth believes in LGBTQ rights.”

For a long time, non-binary marathoners have had no choice but to sigh and momentarily accept the binary.

“I’ve always only been presented with the binary, the ‘M’ or the ‘F,’ ” Riordan says. “And I’ve just gone with the ‘F’ because that is what the powers that be would funnel me into anyway. And I’ve just kind of found a way to not think about it, because I love to run. And I’m not going to let something as silly as one letter on my number stop me from doing it.”

But with the door ajar, they have no interest in going back.

And on marathoning’s biggest stage, they didn’t have to. Donning a mustard-yellow t-shirt proclaiming “queer joy” either side of a rainbow flag and “Danny!” written on their bib (covering a birth name long since discarded), Riordan made the run in the non-binary division. Driven by the promise of peanut M&Ms delivered on the course by friends and the Riordan family race crew (because, why not?) and the Marathon’s famous crowds, they came away with a new personal best.

Plenty remains on the horizon — for Riordan, the running world, and the non-binary and trans community’s place within it. They’ll probably make the physical transition someday, and Riordan knows the world isn’t always an easy place for people like them.

But on Monday, they made the right onto Hereford and the left onto Boylston with a beaming smile, firmly on the road to where — and who — they were always meant to be.

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Amin Touri can be reached at amin.touri@globe.com.