O'Donnell, 50, posted a picture of herself and her second wife Michelle Rounds with the baby to her 587,000 Twitter followers, with the caption, "we r thrilled to announce the arrival of r daughter Dakota."
O'Donnell's publicist said the couple had adopted the baby girl, who was born on January 5, and that "moms and baby are happy and healthy."
O'Donnell has four other children.
The chat show host married Rounds at a quiet ceremony in June in New York. O'Donnell announced their marriage after suffering a heart attack in August.
The comedian, who hosted "The Rosie Show" on Oprah Winfrey's OWN network until it was canceled in March 2012, got engaged to Rounds in front of a studio audience in December 2011.
