The 39-year-old actress and Kopelman, 36, named their new daughter Frankie Barrymore Kopelman.
"Happy to announce that today we are the proud parents of our second daughter," the overjoyed couple told People in a statement.
"Olive has a new little sister, and everyone is healthy and happy!"
Barrymore and Kopelman married on June 2, 2012 in Montecito, California.
Congratulations on the birth of their second daughter!