The woman is believed to have been killed two weeks ago. The body was found on Saturday near a stream in Långshyttan, Dalarna, in central Sweden.
The seven in custody are four men and three women.
The woman was reported missing on June 28th by relatives in Borlänge and, after an initial investigation, police became convinced the woman had been murdered. The police will not say why they suspected murder.
The suspects are men aged 20-45 and women 20-30 years old. Those held are suspected of various degrees of involvement, including harbouring a criminal, accessory to murder and murder.
One of the men admitted through his lawyer during Sunday's court hearing that he was involved in the planning of the crime but he denies the murder charges.
The chief prosecutor, Fredrik Skoglund, says that the suspects are not related to the victim but were acquaintances.
According to the police, the woman was found next to a stream, partially submerged.
Police do not believe the victim was murdered where she was found.
“There were many people involved, and it has been a long time, we think, since the crime was committed, so we have many places to explore,” said a police spokesman.