The baby is Witherspoon's first child with Toth, whom she married in March 2011. She is already a mother to Ava, 13, and Deacon, 8, from her prior marriage, reported People magazine.
"Reese Witherspoon and husband Jim Toth welcomed Tennessee James into their family. Both mom and baby are healthy and the entire family is thrilled," Witherspoon's representative said.
Witherspoon, who initially kept her pregnancy under wraps, later showed off her baby bump at the Cannes Film Festival to lunches and errands at home in Los Angeles.
"Frankly, I'm feeling very round," she had said earlier.