Setting refers to time and place.
To Kill a Mockingbird takes place in the fictional town of Maycomb, Alabama during the 1930s. Several quotes characterize this town as completely affected by the conditions of the Great Depression:
Maycomb was an old town, but it was a tired old town when I first knew it... Somehow, it was hotter then: a black dog suffered on a summer's day; bony mules hitched to Hoover carts flicked flies in the sweltering shade of the live oaks on the square...
... There was no hurry, for there was nowhere to go, nothing to buy and no money to buy it with, nothing to see outside the boundaries of Maycomb County. But it was a time of vague optimism for some of the people: Maycomb County had recently been told that it had nothing to fear but fear itself.
The hints at the absence of money and the news that Maycomb had just been told some famous words help reveal the setting as during the Great Depression. Franklin Delano Roosevelt coined the phrase about only fearing fear when trying to encourage the people of the United States to take heart and trudge through the difficulty of the Great Depression. The references to the heat also allude to that era because the US also experienced a great drought during the early to mid 1930s.
Specific references to the town of Maycomb as well as the county paint the picture of a suburb. There were just enough establishments to help the people trade and keep order.