Illinois State Board of Elections - Voting By Mail
Illinois State Board of Elections - Early Voting before Election Day
Online Register to Vote is available through Early voting for an election cycle. It reopens again a day after the Election Day of an election cycle.
Grace Period Register to Vote is available during Early Voting period
Election Day Register to Vote by bringing 2 forms of ID to your designated polling place
This scenario implies a voter would be casting an "undervote". Casting the ballot, and voting is an imperative to voice our choice, however there are situations, where the recommendation for a candidate is not enough for the voter. In such a scenario, undervote is an option. Here is a brief explanation for an undervote from Ballotpedia.
No, overvote is not an option because it will invalidate the entire ballot. Here is a brief explanation for an overvote from Ballotpedia.
Illinois State Board of Elections - Candidate's Portal