Ethnicity: Her father is a native of Barneveld, the Netherlands, and her mother is an American of half Dutch descent.
Romijn was born in Berkeley, California, United States.
She married actor John Stamos on September 19, 1998. During her marriage, she used the name Rebecca Romijn-Stamos in both her personal and professional life. The couple announced their separation on April 12, 2004, and divorced on March 1, 2005. She has since returned to using her maiden name.
Romijn was asked by Elle magazine in April 2002 whether making Femme Fatale had given her any new ideas about her sexuality. She said, "You know, in my early twenties I wondered if I was interested in women and so I kind of, well ... did my homework. And it turns out I'm pretty straight".
On September 19, 2005, Romijn announced her engagement to actor Jerry O'Connell. They were married on their ranch in Southern California on July 14, 2007. On July 28, 2008, it was announced that Romijn was pregnant Romijn and O'Connell welcomed twin daughters Dolly Rebecca Rose and Charlie Tamara Tulip on December 28, 2008. Dolly is from Dolly Parton's first name and Charlie is for O'Connell's brother.