A-List Celebrities Flock to Beyonce's Belated 41st Birthday Party

Beyoncé's birthday was last week, falling on Labor Day weekend, and since most people were busy -- she seemed ready to party this weekend ... as was the rest of Hollywood.

The stars were out and on the prowl Saturday night ... hitting up a mansion in Bel Air, where Bey and Jay-Z were hosting to celebrate her the big 4-1. It would appear just about anyone who's anyone got an invite -- and they didn't hesitate to take Bey up on her offer to rage.

Huge celebs showed up dressed to the nines for this thing -- folks like Drake, Lizzo, Adele, Rich Paul, Jaden Smith, Bella Hadid, Kris Jenner, Kim K, Tristan Thompson, Khloe, MGK/Megan Fox, Lily-Rose Depp, Offset and even Vanessa Bryant.

Jigga himself also popped up on camera at one point ... but the birthday girl herself never surfaced for a pap photo. We're told people started arriving at 10:30, and stayed 'til about 3.

Take a look through the gallery, and you'll see ... it's a conveyer belt of stardom. If anyone can get famous people together all in one place, it's still Beyoncé. Impressive, no doubt.