Hargitay delivered a baby boy named August by Caesarean section Wednesday in Los Angeles, publicist Leslie Sloane Zelnick said Thursday in an e-mail.
"Mariska and the baby are doing great," she said.
People magazine and Us Weekly reported the baby was a week overdue but Zelnick would not confirm or deny that.
Hargitay, 42, and Hermann, an actor, married in August 2004.
The actress won a Golden Globe last year for NBC's "Law & Order: SVU."
Her mother, blonde screen siren Jayne Mansfield, died in a car crash in 1967. Hargitay's father is former bodybuilder Mickey Hargitay.