The couple now have three children, and their new addition shares a birthday with their son Mason, 5.
Kourtney, 35, posted a message saying she is "blessed and honored" to be Mason's mommy today.
Kourtney and Scott also have a daughter Penelope, 2.
Just last week, Kourtney revealed she was having a boy on her reality show Kourtney and Khloe Take The Hamptons.
She said, "I am so happy we're having a boy," Kourtney says. "It's going to be perfect for our family."
Congrats Kourtney and Scott!
Kourtney's sister Kim is trying for another baby. See what she has to say about giving North West a sibling below.