Occasionally the USPS will mark a package as delivered when it has not yet arrived. This is very rare. If your package states that it has been delivered and you have not yet received it, it is important that you call your local post office right away with your tracking number. If it has not actually been delivered, they can locate it for you. Also, be sure to check around the house, porch, side door, or with neighbors to make sure it wasn’t left there.