As has already been pointed out, the entire story is dripping with irony. There is irony in the setting, in the character's actions and comments, and even in the lottery itself:
It is most ironic that "winning" has a cost, and the cost of winning the lottery is death.
It might be easier to say what isn't ironic about Jackson's classic story!
It is ironic that the children are feeling "liberty" when one of the town is about to be killed.
It is ironic that this killing ceremony is held in the same place and by the same person as the other "civic activities."
It is ironic that the lottery box is such a point of tradition (when it is an object of death).
It is ironic that the townspeople are so casual about where it is stored.
It is ironic that the people part " good-humoredly" for Mrs. Hutchinson when she needs to get through.
Old Man Warner's statement is ironic: "Listening to the young folks, nothing's good enough for them." Being killed isn’t good enough for them?
And of course, that everyone is so concerned about fairness when this is random death we're talking about, that too is ironic.
the story takes place at the begining of the summer season. summer generally begins on june 21th and so 27th is the seventh day of summer.the number 7 is generally considered as a lucky number ,so we can find irony in both both the season of the lottery and the day of it ,both of which represent a blessing event.
we can find irony even on the names of characters , like Mr.summer, who held the lottery.