Greg Peterson's death appeared to be a suicide, The Salt Lake Tribune reported Wednesday.
Police said he had a gunshot wound to his head that seemed to be self-inflicted.
Peterson, 37, was released a few days ago after posting 10 percent of his $2 million bail, The Deseret News reported. He faced a potential life sentence if he was convicted of all counts.
Investigators said Peterson sexually assaulted at least four women and sexually abused a fifth. Most of the alleged assaults involved date rape, and two were said to have taken place at the cabin near Heber City.
Peterson held a barbecue at the cabin July 1, 2011, for the Rocky Mountain Conservatives. The guest list included Utah's two Republican senators, Orrin Hatch and Mike Lee, Rep. Jason Chaffetz, Gov. Gary Herbert and Saratoga Springs, Nev., Mayor Mia Love, who is running for the U.S. House of Representatives.