The novel is set in King's Abbot, a small, fictional village in England. Dr. Sheppard describes the setting at the start of Chapter 2:
Our village, King’s Abbot, is, I imagine, very much like any other village. Our big town is Cranchester, nine miles away. We have a large railway station, a small post office, and two rival “General Stores.” Able-bodied men are apt to leave the place early in life, but we are rich in unmarried ladies and retired military officers. Our hobbies and recreations can be summed up in the one word, “gossip.”
Christie deliberately makes up the name of the village, as well as the name of the "big town" nearby, to make them non-specific. She wants readers to think of it as "very much like any other village," where people have just enough resources to get by but from which most people leave if they have the opportunity. If readers are imagining that the setting is exciting and spooky just because the novel is about a murder, Christie wants them to think again. King's Abbot is usually boring, and the people who live there are just people with too much time on their hands and not enough to do. The fact that the main pastime is gossip makes it an excellent setting for a study in humans and their relationships. Although Roger Ackroyd's spectacular murder incites the plot, the book is also about the way everyone keeps secrets. Even Caroline, the biggest gossip in town, turns out not to know everything about her neighbors.
At the same time, while the setting is nondescript, it is not entirely decontextualized from history or geography. There are plenty of references to popular English books, such as The Mill on the Floss and the works of Rudyard Kipling. A key point in the novel is the recent medical research on cocaine and the somewhat distorted notion that the drug was far more popular in the United States than England at this time. Just like any rural village, it is a misnomer to say that King's Abbott is truly "in the middle of nowhere."