10 ILCS 5/7-46
On receiving from the primary judges a primary ballot of his party, the primary elector shall forthwith and without leaving the polling place, retire alone to one of the voting booths and prepare such primary ballot by marking a cross (X) in the square in front of and opposite the name of each candidate of his choice for each office to be filled, and for delegates and alternate delegates to national nominating conventions, and for committeepersons , if committeepersons are being elected at such primary. A cross (X) in the square in front of the bracket enclosing the names of a team of candidates for Governor and Lieutenant Governor counts as one vote for each of those candidates.
Any primary elector may, instead of voting for any candidate for nomination or for committeeperson or for delegate or alternate delegate to national nominating conventions, whose name is printed on the primary ballot, write in the name of any other person affiliated with such party as a candidate for the nomination for any office, or for committeeperson , or for delegates or alternate delegates to national nominating conventions, and indicate his choice of such candidate or committeeperson or delegate or alternate delegate, by placing to the left of and opposite the name thus written a square and placing in the square a cross (X). A primary elector, however, may not by this method vote separately for Governor and Lieutenant Governor but must write in the names of candidates of his or her choice for both offices and indicate his or her choice of those names by placing a single square to the left of those names and placing in that square a cross (X).
Where voting machines or electronic voting systems are used, the provisions of this section may be modified as required or authorized by Article 24 or Article 24A, whichever is applicable.
10 ILCS 5/7-46