The couple was married in a Brooklyn, New York, courthouse, before a small group of family and friends, E! Newsreports. And the good news about the low-key wedding -- guests were free to dress down!
"When someone gets married in a courthouse, it's really an open invitation to everyone but the beautiful bride to explore all that fashion has to offer," Domino's other sister, Lola Kirke, shared on Instagram. "Here, I try a look simply called 'Pants,' as Cassius goes for 'That Dude from #incubus' and Jemima experiments with 'Off to Therapy!' Congratulations @dominokirke. We love you."
Penn previously dated his Gossip Girl co-star, Blake Lively.
Meanwhile, as Penn and Domino celebrate their Brooklyn marriage, Jemima's own relationship with the New York borough -- at least as it pertains to HBO's Girls -- is coming to an end at the conclusion of the sixth season.
Watch the video below for how the cast has said goodbye, as well as whether a movie may be in the future.