The `Office` actress and husband Lee Kirk became parents to baby Weston Lee on September 24, her representative has confirmed.
The spokesperson added: "Mom and baby are doing great."
Jenna - who married Lee in July 2010 - previously said her pregnancy was going well, through she had experienced some cravings.
She said: "In the beginning, it was a lot of macaroni and cheese and Lucky Charms. Now it`s a lot of strawberries. I`ve been really lucky. I`ve had a really easy pregnancy."
The 37-year-old star revealed she was expecting a boy in July.
When asked by talk show host Jay Leno whether her parents were pleased with the pregnancy, Jenna said: "This is their second grandchild, but first grandson.
"This is the exclusive, Jay. When I went to my movie premiere the other day a reporter asked me if I knew what I was having, and I said I do, but I`m not sharing that yet because I`m [going to] have Jay be the first to know."