“The classic tale of Dorothy in the Land of Oz came from the imagination of L. Frank Baum, who made up the story for his son and a group of children one evening in 1899. When a little girl asked him the name of his magical land with the Scarecrow, Tinman, and Cowardly Lion, he looked around the room for inspiration.
He happened to be sitting next to a filing cabinet with the drawers labeled “A-G,” “H-N,” and finally, “O-Z,” which gave him a quick answer: “Oz.”
Source: The Little Book of Answers