The boy, 3, and his dog went missing Monday from his yard in Custer, the Rapid City Journal reported.
His mother told police that while she was watching her son, she turned around to do something and in a very short time the boy and the dog were gone, Custer County Sheriff Rick Wheeler said.
When police arrived, they tracked footprints made by the boy's boots in the snow and found him and the dog in the woods about a quarter-mile away from home, Wheeler said, adding he couldn't go near the boy because the dog would not allow it.
The dog did not become overly aggressive, but Wheeler said he knew better than to go any closer.
"He was showing me that this was not my area," Wheeler said. "I know that look."
The boy's father took the dog home before safety personnel could approach the boy, who appeared uninjured, but was taken to a hospital as a precaution.
Wheeler said it wasn't clear if the dog was following the boy or the boy was following the dog: "I think it was a joint venture."
The boy was missing for about 55 minutes.