According to the short story "The Lottery," the date is June 27th. The people in the village are coming together for a lottery. They all know what will ensue. Right from the beginning the boys fill their pockets with smooth rocks. Bobby Martin, one of the boys, is named in particular. By the second paragraph, there is a pile of stones. This tells us that the people are ready.
Soon after the men gather. As they do, they talk about taxes, tractors, and farming. The women, then, start to gather as they catch up on the latest gossip. When most of the people are present, they begin the lottery. Mr. Summers comes with the black box and all people draw a piece of paper. The one with the black dot "wins" the lottery. This means that someone in their family will be stoned to death.
In light of this, the people gather for a ritualistic murder. The reason for this is unknown, but it seems that this practice is rooted in a belief that this stoning will cause there to be a good harvest. Here is what one of the characters, Old Man Waner, says:
"Used to be a saying about 'Lottery in June, corn be heavy soon."