Alongside an adorable black-and-white photo of her and Kanye West's youngest child, Kim gushed over her little one.
"Happy Birthday to my baby Chi!!!!" Kim wrote. "The sweetest baby in the whole world! Mommy and Daddy love you so much!"
Chicago's grandmother, Kris Jenner, also took to Instagram to celebrate her granddaughter. Alongside four pics of the munchkin -- where she's cuddling up to her parents and grandma -- Kris called out her "ray of sunshine."
"Happy birthday to our beautiful angel Chicago!! You are my precious ray of sunshine and I love you so very much," Kris wrote. "You put a smile on everyone’s face the moment you crawl into any room and you bring such joy and happiness into our lives!!! I love you Chi Chi 💕 #love #family #happybirthdaychi"
The couple, who are also parents to 5-year-old daughter North and 2-year-old son Saint, recently announced that they're expecting their fourth child via surrogate later this year. This will be the second child that the West family has welcomed with the help of a surrogate, as baby Chicago was delivered that way too.
During an appearance on Watch What Happens Live With Andy Cohen on Monday, Kim revealed that her fourth child would be a boy. Her sister, Kourtney Kardashian, was shocked that she announced the baby's gender, but Kim confessed that she had already let the cat out of the bag.
"I got drunk at our Christmas Eve party and I told some people, and I can't remember who I told, because I never get drunk," Kim shared.
Earlier this month, a source told ET that Kim and Kanye are "excited" to be growing their family.
"The couple has always wanted a big family, and their first time with surrogacy went so well, they decided to do it again," the source said. "The couple is excited to welcome such an incredible gift in 2019. They’ve also talked that after this child, they are most likely done having kids."