I think that one of the horcruxes are located inside of the sorting hat.
I think it could be either the raven claw or hufflepuff item as the horcrux that was put into the hat by Voldemort like the Bones child that has an important role in the books that we haven’t found out why yet. Just like Harry, only a true person from that house could put or pull objects from 1 of the 4 founders into the hat- Harry again the sword of Gryfindor. Bones could have been under the imperious curse (or another student) just to place the horcrux into the hat so that 1 part of the soul is safe from Dumbldor that he would not be able to remove it being from another house. Voldemort had taught the then “Moody” how to trick a very powerful magical item – the Goblet of Fire- and knows how to trick the powerful hat (which is 1 of 2 objects Dumbldor knows to be from Gryfindor).
The horcrux in the hat would complete many circles- Harry’s first use of magic in school, Tom’s first sign of being in Slyth. Tom’s first knowing he is from Salizar. And others….

The horcrux can not be the hat since Dumbldor would know that it was a horcrux since he spent time with the hat- but the hat being a magical object and being owned by Godrick Gryfindor could hold horcruxes and other items that Harry or other students could still remove.
Baiku