10 ILCS 5/24-17

All of the keys of the machine or machines other than those automatically sealed in the machine, shall be placed in the envelopes provided for that purpose, and the envelopes shall be sealed and the envelopes shall designate the serial number of the voting machine to which such keys belong, and the number of the precinct and ward in which such voting machine was used at such election, and such keys shall be returned along with the written statements or returns of such election.