"We are overwhelmed with complete happiness and love having made our eternal commitment," the couple told People magazine. "To say 'I do' in front of family, friends and, most importantly, our children has been the happiest moment of our lives."
Simpson, 33, wore a Carolina Herrera gown at the ceremony before 250 guests. Simpson's sister, Ashlee Simpson was there with fiancé Evan Ross, along with Jessica Alba, Cash Warren, CaCee Cobb and Donald Faison.
Simpson and Johnson began dating four years ago and were engaged shortly after.
2014: The Year in Fashion [PHOTOS]
Polly Bergen, Emmy Award-winning actress, dies