10 ILCS 5/3-1
Every person (i) who has resided in this State and in the election district 30 days next preceding any election therein, or (ii) who has resided in and is registered to vote from the election district 30 days next preceding any election therein and has moved to another election district in this State within said 30 days and has made and subscribed to the affidavit provided in paragraph (b) of Section 17-10 of this Act, or (iii) who has resided in and is registered to vote from the election district 30 days next preceding any election therein and has not moved to another residence but whose address has changed as a result of implementation of a 9-1-1 emergency telephone system and has made and subscribed to the affidavit provided in subsection (a) of Section 17-10, and who is a citizen of the United States, of the age of 18 or more years is entitled to vote at such election for all offices and on all propositions. Any military establishment within the boundaries of Illinois is "in this State" even though the government of the United States may have exclusive jurisdiction over such establishment.
10 ILCS 5/3-1