If Kourtney Kardashian turned 40 you wouldn't know it based on her never-aging looks ... but the big giveaway was her HUGE birthday bash populated by her famous friends.
Kourtney celebrated the big 4-0 Wednesday night in L.A. in one of the most epic celebrations ever, or at least this month. Kim, Khloe, Kris Jenner, Kylie and Kendall were all there ... as was Kanye and TONS of other celebs ... including French Montana, Paris Hilton and Larsa Pippen.