The setting that Jackson creates to begin with is one of great comfort. It is a clear and sunny morning in June. The children gathered in the town square with a feeling of liberty as they had recently finished school for the year. The children gather stones and it seems they have a purpose. The reader is sort of filled with the idea that this is just one of the things that kids do.
As the story moves along, the mood and atmosphere shifts from comfort to unease. The adults begin milling around next and their discussions appear to be forced and less comfortable. The smiles feel forced. It seems that there is some order for the day and the people anxiously, almost nervously await this.
The tone finally shifts one more time in the very end. When the revelation of the lottery is brought to light by the author, a great horror fills readers.