According to E! News, the Keeping Up With The Kardashians star welcomed her second child with partner Scott Disick at the Cedars-Sinai Medical Centre on Sunday 8th July.
Speaking of their new arrival, the couple said in a statement: "Scott and I are overjoyed to welcome our precious angel Penelope Scotland Disick into our lives. We are forever blessed. Mommy and baby are resting comfortably."
It is thought Kardashian had a natural birth, with Penelope weighing 7lb 14oz.
Her mother Kris Jenner later confirmed that Kourtney had an "easy delivery", adding that her new granddaughter looks just like her big brother Mason - who was born in December 2009.
Jenner revealed: "She looks just like [brother] Mason. She's so beautiful. We are so happy."
Kourtney's sister Kim Kardashianalso expressed her happiness over the news, writing on her blog: "Welcome to the world, Penelope Scott Disick! Kourtney gave birth to a beautiful baby daughter on Sunday and the whole family is so thrilled to finally meet her!
"I am so excited to be an aunt again and can't wait to spoil little Penelope. I know Mason is going to be the best big brother in the whole world. Congratulations Kourtney and Scott. Xo"