Weighing 6 lbs., 14 oz., Isabel Ruby Lieberstein was born at 12:50 p.m. Saturday. Among those at the hospital were Kinsey's mother, Bertie Kinsey, and the actress's friend and castmate Jenna Fischer, according to Kinsey's rep, Tess Finkle.
"Mom and baby are doing great!" says Finkle.
Kinsey, 36, announced her pregnancy on her MySpace blog last November.
"They say when you stop trying, that's when it happens – and that's how it went for us," she wrote. Joking about taking prenatal yoga with costar Jenna Fischer, who injured her spine last year, she added: "Between her bad back and my belly, it is the perfect workout!"
Aside from cravings for ice-cold Snickers bars, it appears Kinsey's pregnancy went like clockwork. After attending Kinsey's girls-only baby shower in March--which featured tea sandwiches and white and pink roses--costar Kate Flannery told PEOPLE: "She is a very happy pregnant woman. One of the happiest . . . I have ever seen."