Simpson, 31, began dating former NFL player Eric Johnson, 32, in May 2010. The couple was engaged six months later and announced their baby news last Halloween, People.com said.
"Eric and I are elated to announce the birth of our baby girl, Maxwell Drew Johnson," the message on Simpson's Web site said Tuesday. "We are grateful for all the love, support and prayers we have received. This has been the greatest experience of our lives!!"
Simpson said her daughter weighed 9 pounds, 13 ounces when she was born.