10 ILCS 5/7-43
Every person having resided in this State 6 months and in the precinct 30 days next preceding any primary therein who shall be a citizen of the United States of the age of 18 or more years shall be entitled to vote at such primary.
The following regulations shall be applicable to primaries:
No person shall be entitled to vote at a primary:
In cities, villages, and incorporated towns having a board of election commissioners, only voters registered as provided by Article 6 of this Code shall be entitled to vote at such primary.
No person shall be entitled to vote at a primary unless he is registered under the provisions of Article 4, 5, or 6 of this Code , when his registration is required by any of said Articles to entitle him to vote at the election with reference to which the primary is held.
A person (i) who filed a statement of candidacy for a partisan office as a qualified primary voter of an established political party or (ii) who voted the ballot of an established political party at a general primary election may not file a statement of candidacy as a candidate of a different established political party, a new political party, or as an independent candidate for a partisan office to be filled at the general election immediately following the general primary for which the person filed the statement or voted the ballot. A person may file a statement of candidacy for a partisan office as a qualified primary voter of an established political party regardless of any prior filing of candidacy for a partisan office or voting the ballot of an established political party at any prior election.
10 ILCS 5/7-43