- Democratic congressional and state primaries: open
- Republican congressional and state primaries: open
- Democratic Presidential primary: mixed
- Republican Presidential primary: mixed
- Illinois has nonpartisan registration. There is no option to affiliate with a political party on the voter registration form.
Details of voting in congressional and state primary elections:
- Voters are not required to register with a party to participate in the party primaries, but they do have to publically choose one party's ballot to vote. This is considered a public declaration and can be challenged by other voters.
- Voting history is also public information and records are kept.