Who are the voters who will ultimately determine Chicago’s next mayor?

In the April 4 runoff between Paul Vallas and Brandon Johnson, voter turnout may be what decides the outcome.

Grand Crossing voter
A Chicagoan votes in a voting precinct at St. Moses the Black Athletic Center in the Grand Crossing neighborhood on Feb. 28, 2023. The April 4 mayoral runoff between Paul Vallas and Brandon Johnson could be decided by voters in precincts on the city's South and West sides who preferred other candidates in February. Pat Nabong / Chicago Sun-Times
Grand Crossing voter
A Chicagoan votes in a voting precinct at St. Moses the Black Athletic Center in the Grand Crossing neighborhood on Feb. 28, 2023. The April 4 mayoral runoff between Paul Vallas and Brandon Johnson could be decided by voters in precincts on the city's South and West sides who preferred other candidates in February. Pat Nabong / Chicago Sun-Times

Who are the voters who will ultimately determine Chicago’s next mayor?

In the April 4 runoff between Paul Vallas and Brandon Johnson, voter turnout may be what decides the outcome.

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The race for mayor of Chicago is going to be neck and neck between former CPS CEO Paul Vallas and Cook County Commissioner Brandon Johnson, according to several polls published this past week.

A poll released Tuesday by Northwestern University and a coalition of Black and Latino nonprofits shows the two candidates with equal amounts of support a week ahead of their April 4 runoff election. Three other polls of likely voters show Vallas with single-digit leads over Johnson.

Vallas and Johnson emerged as the top two from a crowded field of nine mayoral candidates in the Feb. 28 general election. Vallas received about 33% of the vote while Johnson finished second with close to 22%.

But nearly half of the Chicagoans who voted in February chose a different candidate, and about 1 million other registered voters sat out the election altogether. Who are those voters, and who will they choose for mayor in the mayoral runoff election, if they decide to vote at all?

A WBEZ analysis of election results from this year, 2019 and 2015 (the two other elections with mayoral runoffs), along with demographic and crime data below, provides a sketch of the votes and voters that may decide what could be a very close mayoral election.

Where do Johnson and Vallas have to make up the most ground?

In February’s election, Vallas had his strongest finishes in precincts on the city’s far Northwest and Southwest sides and some precincts in and around downtown. Johnson saw strong support in precincts on the city’s Near Northwest Side and along the lakefront on the Far North and South sides.

But there are still more than 570 out of the city’s 1,291 precincts where neither Vallas nor Johnson finished first. Nearly all of those precincts are located on the South and West sides in majority-Black and majority-Latino precincts that were most often carried by either incumbent Mayor Lori Lightfoot or Congressman Jesus “Chuy” García.

Lightfoot finished first in about two-thirds of those precincts and García carried nearly another third. Businessman and philanthropist Willie Wilson, who finished fifth overall in February, carried another 14 precincts.

For comparison, in 2015, then-Mayor Rahm Emanuel won 46% of the vote in the general election and García won 34%. There were fewer candidates in that field — just five altogether. And there were far fewer votes up for grabs in the runoff that year: just 21% of voters in the general election voted for a candidate other than Emanuel or García.

In February 2019, however, a whopping 65% of voters chose a candidate other than Lightfoot or Cook County Board President Toni Preckwinkle, the two candidates who qualified for the runoff from a much wider field of 14 contenders that year. In the runoff, Lightfoot captured an overwhelming share of votes — nearly three-fourths — that previously went to other candidates en route to a win with 74% of the vote overall.

Which voters are up for grabs in this year’s mayoral runoff?

The voters who will decide Chicago’s next mayor look very different from the voters who favored either Vallas or Johnson in the Feb. 28 general election, shows a WBEZ analysis of election results and census data.

Voters in precincts where either Vallas or Johnson came in first place were more likely to be white, college-educated, employed, living in households earning more than $100,000 a year and sending their children to private schools. They were also more likely to live in the city’s safest communities.

Capturing support among voters who are up for grabs — the ones in precincts that preferred Lightfoot, Garcia or Wilson — could depend upon how well Vallas and Johnson have shaped their messages to address the unique challenges those voters face with finding work, earning a living wage and dealing with violence. The rates of violent crime in precincts carried by Lightfoot, Garcia or Wilson are far more severe — in some cases, more than 10 times higher — than those in the precincts that Vallas or Johnson carried in the February general election.

What can we expect about voter turnout and preferences in the runoff?

Voter turnout may decide this election, given how close the two mayoral candidates are polling.

There are two main factors that influence voter behavior and turnout, said Dick Simpson, professor emeritus of political science at the University of Illinois Chicago and former Chicago alderman.

“One is that there’s a clear choice between candidates, and the second is that voters think that their vote makes a difference, that the race is close enough that voting matters, and it’s a question of whether that’ll be true this time,” Simpson said.

Turnout for this year’s runoff election will likely vary throughout the city. But there may be a few things we can expect based upon patterns witnessed in Chicago’s two previous mayoral general and runoff elections.

In February, overall, turnout in precincts where either Lightfoot, García or Wilson finished first were lower, by more than 10 percentage points, than turnout in precincts carried by Vallas or Johnson.

If historical patterns hold, the change in turnout between the general and runoff elections for those nearly 600 precincts, where neither Vallas nor Johnson finished first in the general election, will likely be lower than the city’s overall change in turnout. Conversely, in the nearly 700 precincts carried by either Vallas or Johnson, the change in voter turnout will likely surpass the city’s overall change.

In 2019, turnout declined citywide between the February general and April runoff elections by two percentage points, from 35% to 33%, but it declined the most in precincts that neither Lightfoot nor Preckwinkle led in the general election. For instance, turnout in the three precincts Vallas won in February 2019 declined the most, by nine percentage points from 52% to 43%.

In 2015, citywide turnout increased by seven percentage points between the general and runoff elections, from 34% to 41%. Turnout increased the least in the runoff that year amongst precincts that neither Emanuel nor García led in the general election. Turnout in the runoff increased the most, nearly nine percentage points from 31% to 40%, in precincts that García had carried in the general election.

One path to victory for Johnson is to sway and turn out voters in the more than 550 precincts that went to either Lightfoot or García in February. In the 380-plus precincts Lightfoot carried, primarily on the South and West sides, Johnson received 18% of the vote and Vallas 10%. Capturing voters who supported Lightfoot in the general election would provide a boost to Johnson’s chances in the runoff. García endorsed Johnson, but in the roughly 170 precincts García carried in the general election, mostly on the Northwest and Southwest sides, Vallas polled better than Johnson, winning 23% of the votes there to Johnson’s 14%.

Even if Lightfoot and García supporters choose Johnson in the runoff, Johnson might still need a surge in voter turnout in those areas. Vallas may benefit, if turnout declines in those areas. And Vallas might also benefit from Wilson’s endorsement — Wilson placed second in nearly three out of every four precincts that Lightfoot carried.

For Vallas, one path to victory would be to widen his lead over Johnson by increasing turnout in the nearly 500 precincts he led in February’s election, many of which are typically among the precincts posting some of the highest turnout figures in the city. For instance, in February, Vallas was the leading candidate in 125 of the city’s top 151 precincts for voter turnout — where turnout percentages were 50% or more.

Amy Qin is a data reporter for WBEZ. Follow her at @amyqin12. Alden Loury is the data projects editor for WBEZ. Follow him at @AldenLoury. WBEZ’s Ola Giwa contributed to this story.