In the history of the One Piece setting, it is known that the character Joy Boy was the first to seemingly discover the One Piece. It was found on an island at the end of the Grand Line, essentially at the edge of the world. Joy Boy is cited as the first to have this treasure. However, it would be Gol D. Roger of the infamous Roger Pirates who would make it famous by finding it. The One Piece is located supposedly on this final island still that has come to be known as Laugh Tale. Little is known about what the actual One Piece treasure is but there is plenty of speculation. For one, it is possible that the treasure is not even on the island anymore. Or, there is a chance that the treasure was divided up into multiple pieces (ironically) and set around the world. For now, we will just have to wait and see when Luffy and the Straw Hat Pirates find it.