An exposition, in a short story, provides information on the main characters of the story and the setting.
Therefore, in Flannery O'Connor's short story "Good Country People," the exposition ends at the introduction of the main conflict: Joy Hulga's distrust of Manley Pointer.
The exposition, itself, begins with the opening of the story. Mrs. Freeman and Mrs. Hopewell are both introduced. Each of the women have daughters, Mrs. Freeman’s daughters, Glynese and Carramae, and Mrs. Hopewell's daughter, Joy-Hulga, are introduced as well. Another character introduced, a little later in the story, is Manley Pointer.
The exact location of the story, a tenant farm in Georgia, can easily be pictured by the reader given the title, descriptions of the surroundings, and the mentality of the women in the story (stereotypical characterizations provided by O'Connor).
Background is given on Joy-Hulga. Her education in Philosophy and her accident allow readers to understand her mindset and own personal ideologies.
That being said, the exposition ends when Joy-Hulga admits her distrust in Pointer. This is where the rising action begins and the story begins to move toward the climax.