The "Saturday Night Live" alum, 42, who welcomed her fourth child last year, only just filed the birth certificate for her newest family member.
The child, whose name was revealed to be Minnie Ida Anderson, was born on Aug. 1, 2013, according to the certificate obtained by TMZ.
The site said the actress and her longtime partner, director
There was no official record of the child until now, the site said, because the state of California requires only that a child be registered before the kid turns 1.
Minnie joins the couple's other children: Pearl, 9, Lucille, 4, and brother Jack, 3. Minnie is also Pearl's middle name.
News surfaced last September that the "Bridesmaids" star had had the baby, but the tot's gender and birth date were unknown at the time.
However, earlier that month, Rudolph was spotted at LAX toting a swaddled baby in a Bambino carrier, E! News reported. Since Rudolph's third child was already 2 at the time, it probably wasn't him.
The "Up All Night" alum confirmed her fourth pregnancy on "The Ellen DeGeneres Show" in April 2013, but her burgeoning belly had given away her secret before that when she appeared at the 15th Costume Designers Guild Awards in February 2013.
Rudolph is currently filming "The Nest" with former "SNL" costars Tina Fey and Amy Poehler. The film, which revolves around a house party thrown to say goodbye to two sisters' childhood home, hits theaters in December 2015.
She'll also appear in her husband's drama "Inherent Vice," due in January 2015, and Peer Pederson's "The Greens Are Gone."