Fond du lac police discovered Katie Gensmer’s body Wednesday morning near the parking lot of the New Fane trail in the town of Auburn.
The 18-year-old had died from a fatal stab wound to the heart.
The Fond Du Lac county sheriff says the man arrested was discovered alone at a campsite only five miles from the trail where the murder occurred.
Detectives were led to the suspect after Gensmer’s family saw the two together Tuesday night.
The suspect is expected to be in court next week.