As I Lay Dying is the story of Addie Bundren's family, who must bring her body to Jefferson to be buried after she dies. Anse, Addie's husband, Cash, Darl, Jewel, and Vardaman, her four sons, and Dewey Dell, her daughter, face many obstacles on their journey, as each simultaneously attempts to resolve their own personal issues. The novel explores death, identity, and meaning through the Bundren family's relationships to each other.
The book is narrated by 15 different characters over 59 chapters. It is the story of the death of Addie Bundren and her poor, rural family's quest and motivations– noble or selfish – to honor her wish to be buried in her hometown of Jefferson, Mississippi.
As the book opens, Addie is alive, though in ill health. Addie and others expect her to die soon, and she sits at a window watching as her firstborn, Cash, builds her coffin. Anse, Addie’s husband, waits on the porch, while their daughter, Dewey Dell, fans her mother in the July heat. The night after Addie dies a heavy rainstorm sets in; rivers rise and wash out bridges the family will need to cross to get to Jefferson.
The family's trek by wagon begins, with Addie’s non-embalmed body in the coffin. Along the way, Anse and the five children encounter various difficulties. Anse stubbornly refuses to accept any charity, including meals or lodging, from people, so at times the family goes hungry and sleeps in barns. Jewel, Addie’s middle child, tries to leave his dysfunctional family, yet cannot turn his back on them through the trials. Cash breaks a leg and winds up riding atop the coffin. He refuses to admit to any discomfort, but the family eventually puts a makeshift cast of concrete on his leg. Twice, the family almost loses Addie’s coffin – first, while crossing a river on a washed-out bridge (two mules are lost) and, second, when a fire of suspicious origin starts in the barn where the coffin is being stored for a night.
After nine days, the family finally arrives in Jefferson, where the stench from the coffin is easily noticed by the townspeople. In town, family members have different items of business to take care of. Cash’s broken leg needs attention. Dewey Dell, for the second time in the novel, goes to a pharmacy, trying to obtain an abortion that she does not know how to ask for. First, though, Anse wants to borrow some shovels to bury Addie, because that was the purpose of the trip and the family should be together for that. Before that happens, however, Darl, the second eldest, is seized for the arson of the barn and sent to the Mississippi State Insane Asylum in Jackson. With Addie only just buried, Anse forces Dewey Dell to give up her money, which he spends on getting "new teeth", and decides to marry the woman from whom he borrowed the spades.
As is the case in much of Faulkner's work, the story is set in Yoknapatawpha County, Mississippi, which Faulkner referred to as "my apocryphal county," a fictional rendition of the writer's home of Lafayette County in the same state.