The boy, Prince McCree, was reported missing on Wednesday afternoon, according to the Milwaukee police. The boy's body was located on Thursday.
Police are currently investigating a cause of death, and said the investigation was being treated as a homicide.
The child was last seen at his home on Wednesday morning. His parents realised he was missing around 1pm on Wednesday, and traveled door-to-door asking after him that evening, according to the Milwaukee Journal Sentinel.
Police issued a "critically missing" alert for the boy around 8.30pm that evening. An Amber Alert was not issued because police did not have enough information about a potential suspect or vehicle to pass along to the public.
The dumpster where his body was found was approximately a mile away from his home.
In addition to the 15-year-old, a 27-year-old man was also taken into custody. Both are being treated as "persons of interest," meaning they are not currently considered suspects but individuals who may have more information on the child's disappearance and death.
State Senator LaTonya Johnson, who lives near the family, told the Milwaukee Journal Sentinel that the two persons of interest lived in the child's home, but said she was not aware of what relation they have to the family.
“They were distraught,” Ms Johnson said of the family. “It was a shock. This neighborhood is relatively quiet. You don’t see a lot of police activity. We knew it was something serious.”
A member of the neighborhood block watch told the paper that Prince had been seen earlier on Wednesday playing with other children, but did not have further details regarding his disappearance.
City Alderman Michael Murphy, who represents the neighborhood where the incident took place, said the city's residents would likely be traumatised by the boy's death.
“It’s a terrible tragedy for the whole community to see another child so senselessly lose their life and then to be discarded in the manner in which they found the child,” he told the paper.
This is the second homicide involving a child in Milwaukee in several weeks. Earlier this month, 12-year-old Jarice Robinson was found dead in his home on the northwest side of the city. He was found malnourished and his body was in an advanced state of decay when it was located.
His father, Ramuan Moye, 45, was charged with four felonies in connection to the boy's death.