SAG: Inside Star-Studded ‘People’ Bash

While Hollywood’s biggest night, the Academy Awards, isn’t for a few more weeks, the winners and nominees of Sunday evening’s Screen Actors Guild Awards got down at an exclusive (and insanely attended) after party.

People Magazine and Grey Goose Vodka sponsored the bold-name fest, that boasted superstar attendees like Brad Pitt and Angelina Jolie.

“They came and went very quickly,” an insider tells Celebuzz. “Brad stopped for a beer and a few hellos, then he and Angelina slipped out the back.”

While Brangie departed to tend to their brood, there were plenty of proud parents in the place. Alec Baldwin’s daughter Ireland never left the Best Actor’s side. The two worked the entire party tent next to the Shrine Auditorium as a pair, giggling and whispering to one another.

Meryl Streep also showed off her son and daughter to the room, only once ditching them to embrace Tina Fey in a massive hug. The actresses fussed over one another for a few moments, winners for their work in Doubt and 30 Rock, respectively.

Fey’s buddy Amy Poehler did a little partying with husband Will Arnett, deservedly so after winning her body back post-baby.

“Amy was indulging a bit, drinking and smoking,” the source said.

She wasn’t alone in revelry: Famous cast mates huddled together and let their hair down. From Entourage and 30 Rock to Slumdog Millionaire and The Office, a buzzing hive of busy actors enjoyed their coworkers and peers.

Big Mad Men winner Jon Hamm looked a bit aloof, however.  An onlooker dishes that Hamm spent most of his night alone drinking and smoking in a corner. Hamm walked the red carpet with wife Jennifer Westfeldt, but she was nowhere to be seen at the bash.

Other couples held court, however, like Jamie-Lynn Sigler and Jerry “Turtle” FerreraUgly Betty star America Ferrera (no relation) and Ryan Piers Williams, a stunning Claire Danes and her thesp beau Hugh Dancy, Jeremy Piven and a young blonde as well as Harvey Weinstein and bride Georgina Chapman.

And while all these matches no doubt thrill, our favorite shmooze-crew happened backstage at the awards telecast, where spies tell us Sean Penn and Josh Brolin puffed on cigarettes while chatting with Katie Holmes.

While Katie’s most recently been on Broadway’s clock, clearly she’s a Hollywood girl at heart.