Sulli was already dead when authorities arrived at the scene, according to police.
Police said a report was filed by a staff member at her agency at around 3:20 p.m.
The agency staffer, who visited Sulli’s home in Seongnam, Gyeonggi Province, discovered Sulli’s body in her bedroom on the second floor.
The agency employee had gone to the two-story house after phone calls to the entertainer went unanswered, although she had an engagement on Monday. Their last telephone call ended at 6:30 p.m. on Sunday.
Police and the emergency crew arrived about nine minutes after the report was received and an onsite inspection revealed that rigor mortis had set in.
Paramedics did not perform CPR.
The police station has referred the case to the forensics service.