Sam Rockwell was born on November 5, 1968, in San Mateo, California, the only child of two actors, Pete Rockwell and Penny Hess. The family moved to New York when he was two years old, living first in the Bronx and later in Manhattan. When Sam was five years old, his parents separated, at which point he and his father moved to San Francisco, where he subsequently grew up, while summers and other times were spent with his mother in New York.
He made his acting debut when he was ten years old, alongside his mother, and later attended J Eugene McAteer High School in a program called SOTA. While still in high school, he got his first big break when he appeared in the independent film Clownhouse (1989). The plot revolved around three escaped mental patients who dressed up as clowns and terrorized three brothers home alone--Sam played the eldest of the brothers. His next big break was supposed to have come when he was slated to star in a short-lived NBC TV-series called Dream Street (1989), but he was soon fired.