The 35-year-old reality star and her longtime love, Scott Disick, are also the parents of Penelope, 2.
Before going into labor, the Keeping Up With the Kardashians star shared a picture of a baby doll lying in her newest addition's crib on Instagram on Saturday, captioning the image, "Nap time! Someone's already using our new crib."
The name has yet to be announced. Disick seems to want traditional, named after one of their deceased fathers, and Kourt likes to go the Hollywood route.
Whatever you do, don't call Barbara Walters retired.
The 85-year-old may have stepped down from The View panel in May, "[But I'm] not exactly slowing down," she tells People.
In addition to hosting her 10 Most Fascinating People special, which aired Sunday night, Walters says she's having no trouble filling her days.
"I'm working relatively little," she says. "I sleep until 9 o'clock some days! I go out to lunch with friends. I travel. When I was on The View I was working every day, so this is a very mild schedule for me."
Walters still serves as co-executive producer on the ABC talk show.
In mama mode
Drew Barrymore looked every inch the happy mama Saturday, bringing her daughters to a children's charity event in Los Angeles.
With her youngest, Frankie, born in April, strapped to her chest, Barrymore, 39, posed happily with her former Never Been Kissed co-star and Baby2Baby charity host Jessica Alba, whose The Honest Company sponsored the event.
Also joining in at the party's craft table was Barrymore's oldest daughter Olive, 2, who rounded out the happy family outing (Barrymore's husband Will Kopelman also attended).