In general, the setting of a novel comes down to two general items.  Where does the story take place, and when does the story take place?  

Shiloh by Bobbie Ann Mason takes place in western Kentucky. Specifically, the novel takes place in a fictionalized area near the real towns of Mayfield and Paducah. Bobbie Ann Mason placed many of her stories in that area, because it is the area where she grew up.  By writing about areas that are familiar to her, she keeps the story grounded in reality and makes it feel more real to her readers.  

The time period that the story takes place during is the 1970s.  The time period is important because a lot of change is happening across the country at the time.  The Civil Rights movement has just wrapped up and the booming 80s are coming on the horizon.  Beliefs and value systems are rapidly changing.