Barnett was visiting his paternal grandparents' home on August 31, 1982. They lived on Hillcrest Farms, an egg and dairy farm in the Grangeville, Idaho area. The farm was seven miles north of Grangeville and encompassed several hundred acres. Barnett had been staying there for a couple of weeks with his father; his mother was in southern Idaho.

Barnett was last seen sitting in a hay wagon in front of one of the chicken barns while dozens of workers were unloading a delivery of chickens. He has never been heard from again. His family started searching for him only fifteen minutes later, but no one found any clues as to his whereabouts, and called the police at 10:30 a.m. Bloodhounds tracked his scent to a fence line on the northwest part of the farm, then lost the trail. An extensive four-day search of the farm, involving 250 volunteers, turned up no sign of the child.

Barnett's grandparents, Waldo and Martha McChoard, were suspects in his disappearance for almost two decades afterward. Martha reportedly acted oddly and she failed a polygraph exam. She was known to dislike Barnett's mother, and police theorized she took Barnett and gave him to someone else to raise. Martha took another polygraph in May 2001, and was cleared of an involvement in Barnett's case. Waldo also agreed to take a polygraph, but he died before the exam could take place.

Barnett's parents live in Oregon and his mother has been active in the search for him. His disappearance remains unsolved.