The model's milestone birthday was on Saturday, and she's been celebrating in Las Vegas alongside her 36-year-old boyfriend, Scott Disick, as well as her close friends, including Kylie Jenner. On Saturday, she kicked off the festivities with a celebration at Encore Beach Club at Wynn Las Vegas, where she was greeted by a banner with her name on it, custom pillows with her dog, Hershela's, face printed on it and enlarged life size cut outs of herself. She was later treated with cupcakes that also had Hershela's face on them, which read "Happy Birthday Sofia."
Richie rocked a Chanel bathing suit at the pool party, while Disick wore a black button-up and shorts. Richie's friends Anastasia Karanikolaou, Yris Palmer, Amber Asaly and Victoria Villarroel were also present.
Later in the night, Richie had dinner at Cipriani Las Vegas in Wynn Plaza with her group of friends, including Kylie Jenner. A source tell ET the group enjoyed family style courses and a champagne birthday toast with Perrier-Jouët. After dinner, the group headed to XS Nightclub at Wynn Las Vegas where the Chainsmokers were performing, and Richie -- who looked incredible in a sparkly pink jumpsuit -- was greeted with a "Happy Birthday" display, drummers and a confetti parade with a massive cake.
At one point in the evening, Drew Taggart from the Chainsmokers had the birthday girl join him on stage and had the entire venue sing Happy Birthday. The source says Richie stayed on stage with her girls dancing, jumping around and taking shots with the group.
The source adds that Jenner arrived later wearing a skin tight pink latex dress and the girls danced together and were singing along to the Chainsmokers' set. At one point, the source says Jenner lifted up Richie and twirled her around.
"I think you really got to figure out what's important to you at the end of the day," Disick shared of how he and his ex make it work. "I mean, there's so many different things that can pull you in different directions. You could look online, and Instagram, and social media, all these things, but at the end of the day -- I mean, you just want to be happy, you want to be content, you want to be comfortable. You want to love the people you are with."
"It's hard work for all parties -- I think for you, Kourtney, Sofia, they're all just really strong," she chimed in. "I'm really proud of all of them. ... I'm so proud of them, and I'm so proud of them promoting that and hopefully inspiring other people. It's a beautiful thing to get along with each other and for your kids to see that."