Set in mountainous Sevier County, Tennessee, in the 1960s, Child of God tells the story of Lester Ballard, a dispossessed, violent man whom the narrator describes as "a child of God much like yourself perhaps". Ballard is violently evicted from his home, which is sold at auction to another Sevier County resident, John Greer. Now homeless, Ballard begins squatting in an abandoned two-room cabin and voyeuristically spying on young couples in their cars near the Frog Mountain turnaround. Ballard is falsely accused of rape by a woman he finds sleeping along the roadside, and is jailed for nine days. Interspersed among the narrator's story are townspeople's accounts of Ballard's early life, revealing his early violent behavior and the suicide of his father.
While out squirrel hunting, Ballard comes across a dead couple in an idling car. He steals the couple's money, rapes the woman's corpse, and stores her body in the attic of his cabin. Ballard's cabin burns down with the corpse inside, and he moves his remaining possessions into a nearby cave. Ballard visits his friend's home, finding only the friend's daughter and a disabled child. When the daughter rejects his sexual advances, he kills her and sets the house ablaze, storing her body in the cave. Later, Ballard shoots a couple in their car. As he flees the scene with the woman's corpse, he sees that the man survived and drove away. Prompted by the string of murders, the county sheriff begins investigating Ballard. The county floods, and the sheriff recalls the county's history of vigilantism with the Whitecaps and Bluebills.
Ballard unsuccessfully attempts to kill John Greer, the current owner of his former home, and is shot in the process. He wakes handcuffed to a guarded hospital bed. One night, a group of men appear in his hospital room demanding to know where he stored his victims' bodies. Ballard initially feigns innocence, but offers to lead the men to the bodies when they threaten to hang him. Ballard brings them to the cave, where he escapes through a crevice too small for the other men to fit through. For three days, Ballard deliriously roams the cave searching for an exit. He eventually chips through a small crack to the surface and returns himself to the hospital.
Instead of facing trial, Ballard is sent to a mental hospital where he contracts pneumonia and dies soon after. His remains are dissected by medical students in Memphis for three months before he is buried. In the spring of the same year, a farmer's plow falls into a sinkhole in Sevier County, revealing a cavernous chamber containing the bodies of seven of Ballard's victims.
