Resolves to the candidate with the most votes in the 2028 Republican presidential primary or caucus in Illinois, per certified state or party results, or an AP call once the outcome is settled. Caucuses and ranked-choice contests count final-round votes. If no vote totals are reported, the one awarded the most delegates wins.

If the state and the party hold separate contests, the one that awards delegates counts. Uncommitted resolves to its own answer if listed, otherwise Other. N/A if no Republican contest is held in Illinois before the nominee is chosen.