The little girl, named Frankie Barrymore Kopelman, was born on 22 April.
In a statement Drew and Will said: "Happy to announce that today we are the proud parents of our second daughter, Frankie Barrymore Kopelman. Olive has a new little sister, and everyone is healthy and happy!"
The actress was overjoyed to announce that she was pregnant with her second child in November and confirmed she was having a baby girl just a month later.
Speaking on a chat show after the first birthday of their eldest daughter Olive, Drew explained that she was an only child and would prefer to have a big family. The Hollywood star admitted she was already planning for another baby.
She said she was looking forward to holidays like that taken by the family in the comedy National Lampoon's Vacation. In the film Audrey and Clark Griswold's road trip is beset by mishaps when they head for an amusement park.
"I want to be the Griswolds," she said. "I want the kids in the back rolling their eyes at mom and dad. I want Clark and Audrey, theme parks and the whole nine (yards)."
The fun-loving mum explained that Olive was named because of a reference in a baby book that said at one point the developing baby was the size of an olive.
She also pointed out that the name is an anagram for "I love," saying, "So that's gotta be auspicious."
A former wild child, the actress has become a homebody with the help of her husband and his family. Soon after marrying Will in 2012, the star said "had won the in-laws jackpot" and credited his traditional upbringing for motivating her to have family dinners.
She said: "I never had dinner with my mom or dad, let alone together. It's amazing to think that in life you can completely have a do-over.
"Family dinners would never have occurred to me, and that's what I want most now."
Drew has been keeping busy in the run up to the birth by publishing Find It in Everything, a book of photographs she has taken over the last decade. The 'it' referred to in the title is the shape of a heart as it appears in everyday objects and fun snaps.