10 ILCS 5/20-7

Upon receipt of such vote by mail voter's ballot, the officer or officers above described shall forthwith enclose the same unopened, together with the application made by said vote by mail voter in a large or carrier envelope which shall be securely sealed and endorsed with the name and official title of such officer and the words, "This envelope contains a vote by mail voter's ballot and must be opened on election day," together with the number and description of the precinct in which said ballot is to be voted, and such officer shall thereafter safely keep the same in his office until counted by him as provided in the next section.