"Happy birthday to my mini me! I can't believe you are 4 already. I love you so much, Northie!" she wrote on her website.
Kardashian's mom, Kris Jenner, and sister Kylie Jenner were among those to also wish North a happy birthday online.
"Happy birthday to our beautiful, funny, smart little love bug, North," Kris wrote on Instagram.
"You bring so much light to our lives and I am blessed beyond words to have you as my granddaughter. It brings me so much joy to watch you grow up to be sweet and kind and loving... I love you so much my precious angel girl."
"Happy birthday to this cutie," Kylie added on her own account.
She recently confessed she fears her grandchildren will be bullied because of her family's fame.
"It's my grandchildren who I worry about because I have six of them; the oldest just turned 7, and my youngest is 6 months old, and they don't have a choice about [celebrity]," the star told The Hollywood Reporter. "And I worry, I do, because it is such a bullying environment."
Kardashian and her family came to fame on the E! series "Keeping Up With the Kardashians," which completed a 13th season this week.
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