Joy is from an older generation of word names, which also included Merry, Bliss, and Glory -- all of which exert a certain amount of personality pressure on a child. One interesting name that means the same thing: Chara.
Joy began to be used as a name by the seventeenth century Puritans, with the idea of "being joyful in the Lord." It came into more general use in the late nineteenth central, part of the revival of virtue names. Her high point was in 1974, when she reached Number 109 on the charts; she's now at Number 462. Joy has also been often used as a middle name. One recent bearer: comedian/TV personality Joy Behar.