"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.
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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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