March 17 marks the 2026 primary, where voters can pull a Democratic or Republican ballot to pick who appears on the ballot come November. All voters, partisan or not, can weigh in on referendum questions.

Monday was the first day for candidates from established parties to file election petitions for the March 17, 2026 primary. The last day is Nov. 3.

Democratic U.S. Rep. Lauren Underwood of Naperville has one fewer potential Republican challenger to worry about in 2026.