What is a runoff election, and does Illinois use that system?

The hotly-contested U.S. Senate primaries in Texas have once again brought the question of runoff elections to the forefront of American politics.

Texas is one of a handful of U.S. states that employ runoffs in primaries and general elections, and there will be at least one for voters to consider in the weeks ahead.

That will be a runoff for the Republican nomination in Texas’ U.S. Senate race, as neither Sen. John Cornyn nor Attorney General Ken Paxton received 50% of the vote in Tuesday’s primary in the state.

Democrats did manage to avoid a runoff in their Senate primary, as state Rep. James Talarico defeated Congresswoman Jasmine Crockett in the party’s primary.

Republicans fully expect the runoff election, to be held May 26, to be costly and contentious, with both candidates unloading a fusillade of attack ads and verbal swipes at one another during the primary season.

So what is a runoff election? How many states employ them? Is the state of Illinois one of them?

Here’s what to know.

What is a runoff election?

In most cases, a runoff election occurs when a candidate in a particular race fails to win a majority of the votes. This generally happens in a race with three or more candidates, but can also occur if a candidate has a strong write-in vote total.

Some states have slightly different rules for runoffs. According to the National Conference of State Legislatures, North Carolina holds runoffs in elections if no candidate receives at least 30% of the vote in an election, and that runoff must be requested by the second-place candidate.

In South Dakota, the threshold is 35% of the vote for an automatic runoff.

In most of the states that use runoffs like Texas, runoffs are held between the top two candidates in an election if a candidate doesn’t receive at least 50% of the vote.

How many states use runoffs?

According to the NCSL, a total of nine states use runoffs in some fashion during primary elections. Seven of those use the 50% rule, while North Carolina and South Dakota have different rules.

Three of those states, Georgia, Louisiana and Mississippi, employ runoffs in general elections as well.

So Illinois doesn’t use runoff elections?

At the state level Illinois does not use runoff elections, but the city of Chicago does when selecting its mayor.

If no mayoral candidate receives a majority of the vote in the first round of voting, typically held on the last Tuesday of February in odd-number election years, then a run-off is held between the top two candidates at the beginning of April.

The last three Chicago mayoral elections have come down to runoffs. Former Mayor Rahm Emanuel defeated current Rep. Jesús “Chuy” García in the 2015 runoff for mayor, while former Mayor Lori Lightfoot defeated Cook County Board President Toni Preckwinkle in 2019.

Mayor Brandon Johnson defeated Paul Vallas in the 2023 runoff election.