Tripplehorn was born in Tulsa, Oklahoma to Tom Tripplehorn (known as "Tommy Tripplehorn"), who was once a guitarist with Gary Lewis & the Playboys. After graduating high school, Tripplehorn became a D.J. at Tulsa radio station KMOD, using the air name "Jeanie Summers". She was stage-trained as an actress (at Juilliard) and also served as a TV host.
Tripplehorn was engaged to actor Ben Stiller for a time. She is now married to actor Leland Orser; the couple have a son, August, born in 2002. Tripplehorn's grandmother, Jean Neely, appeared in the film Reality Bites, in which Tripplehorn also had a role.