Perry Edward Smith
- Along with Dick, one of the two murderers of the Clutter family. He is a short man, with a large torso but small legs. His legs were badly injured in a motorcycle accident. He wants very much to be educated, and he considers himself quite intelligent and artistic. His childhood was lonely and disorganized. His criminal record seems to be a natural extension of the strange environments in which he grew up.
Richard Eugene Hickock
- Along with Perry, one of the two murderers of the Clutter family. Also a small man, Dick grew up in Kansas, was married twice, and is jailed for passing bad checks. He is a practical man who exudes confidence and cruelty, but in reality he is not as ruthless or brave as he seems.
- The father of the Clutter family. His wife is Bonnie. He has four children: two older daughters who have moved out, and Nancy and Kenyon. His large property, River Valley Farm, keeps him moderately wealthy. Starting with little, he has built up a large, successful farm. He is a community leader, involved with many organizations. He is a gentle man, a strict Methodist. He served on the Federal Farm Credit Board under President Eisenhower.
- Herbert's wife, Bonnie, cannot keep up with his public image as a leader, and she withdraws into the home. Suffering depressive mental disorders, she spends a great deal of time in bed.
- Along with Kenyon, one of the two youngest Clutter children. They both still live at home. She is "the darling" of the town, a class president and future prom queen. Like her father, she is very organized.
- An awkward 15-year-old, Kenyon loves to tinker with carpentry and machines.
- Nancy's steady boyfriend, Bobby lives nearby.
- An investigator for the Kansas Bureau of Investigation (KBI), Dewey is the agent responsible for much of western Kansas. He becomes very involved in the case, to the distress of his wife, Marie, and his two small boys.
- One of Dewey's principal KBI assistants. Nicknamed "Brother Nye," he is the youngest of the group. During the capture and interrogation of Smith and Hickock, he has the flu.
- The oldest of the KBI assistants, Church is nicknamed "Curly" and is supposedly the fastest draw in Kansas.
- Another of the three KBI assistants, Duntz is a burly man with a broad face.
Tex John Smith
- Perry's father, Tex is a kindly backwoodsman who taught Perry to bake bread, but who never comes to see his son in jail. Perry's mother is Flo Buckskin, who Tex met and married on the rodeo circuit.
- Nancy's best friend, Susan lives in Holcomb.
- Assistant to the chaplain of Lansing, the Kansas state prison, Willie-Jay becomes a kind of mentor to Perry. He tells Perry that he is talented.
- An inmate at Lansing prison. After Perry leaves on parole, he became Dick's cellmate. He is a former employee of Herbert Clutter, and he tells Dick about the ranch and the layout of the house.
Lowell Lee Andrews
- Andrews was a young college student who murdered his family. He is a schizophrenic. Several of his years on death row overlap with those of Dick and Perry. Perry resents the fact that Andrews is highly educated.
- An employee of River Valley Farm.
- An employee of River Valley Farm. He and his wife live on the property.
- The proprietor of Hartman's Cafe. She has a thick skin and scolds her customers when they gossip too much about the Clutter murders.
- Perry's only living sister. She lives in San Francisco and is married.
- An old army friend of Perry's who starts a correspondence with him upon reading about the case in the newspaper.