After a day of preparing and pampering, the superstar singer was ready to party.
Dressed in a white bustier crop top that showed off her perfectly-toned abs, she arrived with best friend Leah Remini for a bash at Nammos, a Mediterranean restaurant in Southampton, New York, Thursday night just as DJ Cipha Down was spinning "Jenny from the Block."
"She was so happy and she stayed till 4 a.m.," a source tells PEOPLE. "They had a dinner party and there was champagne, and she danced all night long. Everybody was dancing."
The guest list of about 60 people, according to the source, included Khloé Kardashian and her boyfriend French Montana, Rachel Zoe and Rodger Berman, Kelly Ripa and Mark Consuelos, Brian Atwood, Fat Joe, Russell Simmons, Andy Cohen, Scott Disick and Lopez's mother, Guadalupe Rodriguez, her sister, Lynda, and her longtime manager, Benny Medina, who gave a heartfelt speech about the singer during the dinner at the restaurant, which was decorated in shades of blue.
"Turnt up in the Hamptons happy b-day to the queen," French Montana wrote in an Instagram post of him and Lopez at the party.
"She served it last night!!!" Kardashian wrote. "Happy birthday."
Fat Joe posted a photo of the decadent birthday cake, created by Sami Cakes, which depicted Lopez in her famous blue-green Versace dress atop a lion.
Maksim Chmerkovskiy, who's been spending time with Lopez since her split from Casper Smart, also showed up before the end of the night. But a source tells PEOPLE of Maks and J.Lo, "They are friends."
Reporting by LIZ McNEIL