The Douglas County High School in Castle Rock was locked down for about an hour Tuesday after the body of a 17-year-old student was found in the parking lot.
Douglas County sheriff's Deputy Cocha Heyden says foul play isn't suspected in the boy's death.
School district spokesman Bruce Caughey says the student apparently died before school began, but wouldn't give more details.
An autopsy is planned.
Grief counselors and members of the district's crisis team were at the school. School officials also were drafting a letter about the incident for students to take to their parents.