Mary McCormack Welcomes a Daughter
09/11/2011 AT 08:05 PM EDT
Mary McCormack, who hunts down witnesses on In Plain Sight, delivered her third daughter, Lillian, on Saturday morning, Sept. 10, her rep confirms to PEOPLE.
Lillian weighed in at 6 lbs., 15 oz. and is 20 inches long.
The actress, 42, and husband Michael Morris’s new arrival joins big sisters Rose, 4, and Margaret, 7.
McCormack – who gave PEOPLE a tour of her trailer on-set – had her pregnancy written into the storyline of her character Marshal Mary Shannon. – Julie Jordan