The characters in William Golding's Lord of the Flies are all English schoolboys; they are on an island because their airplane crashed in a skirmish during World War II.
The boys range in age from five or six to about thirteen; there are no adults on the island, so in chapter one when they decide to choose a leader, their choices are limited to the older boys. Two logical choices quickly emerge: Ralph and Jack.
Ralph has demonstrated absolutely no leadership skills; in fact, he has seemed more concerned about just enjoying life without any adults. Jack, on the other hand, has significant leadership experience. He is the leader of an entire choir, and it is clear from the beginning that he is used to giving the choirboys orders and being obeyed.
When the vote is taken, Jack assumes he will be the obvious and overwhelming choice; however, the choir does not seem at all interested in voting for him at first. (Obviously they have already experienced at least some of the cruelty Jack later exhibits.) "With dreary obedience the choir raised their hands" for Jack.
Ralph looks like a leader, though, and the younger boys all vote for him. Ralph appeases his disgruntled rival by offering to let him be chief of the hunters (most of his choirboys).
While no specific names are listed during the vote, the text clearly says that the entire choir raised their hands for Jack. Since Simon is a member of the choir, we can infer with near certainty that he voted for Jack.