Tyler Hadley, 17, faces two counts of first-degree murder in the deaths of Blake and Mary-Jo Hadley.
Police believe the teenager bludgeoned his parents with a hammer and then left their bodies in the master bedroom.
Dozens of people attended the party advertised on Facebook, apparently unaware of the bloody scene locked away in the house, police said.
The party was loud enough to prompt a noise complaint and a visit by police officers. When they arrived at 1:30 a.m. Sunday to warn about the noise, police said the party was already breaking up.
Then, police said, they received a tip that a slaying may have taken place. They returned to the home at 4:20 a.m., finding the bodies covered with towels, files, books and other household items, and the hammer between them.
Autopsies were under way, but police said they believed they died of blunt-force trauma.
A teen, who did not want to be identified, said he didn't suspect anything when he attended the party, although the suspect had informed the partygoers that they were not to go in any of the rooms.
A motive has not yet been determined.
The Associated Press contributed to this story.
