The former The Hills star and husband Jay Cutler, quarterback for the Chicago Bears, are now parents to three children.
"Saylor James Cutler was born today at 1:32PM," Cavallari announced on Instagram Monday.
Saylor joins two older brothers: Jaxon Wyatt, 18 months, and Camden Jack, 3.
"She's going to steal Jay's heart, which will in turn melt mine!" Cavallari, 28, said recently, according toPeople. "I'm excited for the boys to grow up with a sister. I think it will help them to better understand and respect women."
The fashion designer and Cutler had picked out their daughter's name years ago, and you'll never guess how they stumbled across it.
"We picked out this baby girl's name when I was pregnant with our first," Cavallari said in September. "I met a woman and her dog, and I loved her dog's name. Funny enough, it was the name she had picked out if she had a girl, but she had boys, so she used it for her dog instead."
Cavallari, whose book Balancing in Heels will be released in March of next year, revealed she was pregnant for the third time this past May. She announced the baby's sex just two months later by posting a picture of pink Converse sneakers on social media.
Cutler proposed a total of three times to Cavallari -- who also competed on Dancing with the Stars' thirteenth season -- because they had an on-again, off-again relationship for a while.
The Hills aired on MTV from May 2006 to July 2010. Cavallari gave birth to Saylor only three days after her former co-star Audrina Patridgegot engaged to longtime boyfriend Corey Bohan, a pro BMX dirt bike rider.