Eileen O'Neill Burke won the razor-thin primary for Cook County state's attorney. How did she do it?

This year’s Democratic primary for Cook County state’s attorney will be remembered as one of the narrowest local primary election wins in recent memory.

Eileen O’Neill Burke just barely squeaked past Clayton Harris III in a race where the outcome wasn’t decided for nearly two weeks. In heavily Democratic Cook County, O'Neill Burke, who will face Republican nominee Bob Fioretti in November, is all but assured to be the county’s next top prosecutor.

Speaking to reporters during a Monday morning press conference, O'Neill Burke said she intends to provide Cook County residents with the level of public safety they desire.

“I spoke to people all over the county, all over the city. And what unites us is more than what divides us. People told me, everywhere, they want to be able to go out at night and not be worried,” O'Neill Burke said. “They want to ride on a safe public transportation system. People want illegal guns and assault weapons off of our streets. Those are all things we all want. We can do that. We can move this county forward. Whether you voted for me or not. I'm promising today that I will work tirelessly as your state's attorney.”

While O'Neill Burke’s overall margin of victory was incredibly small — about 1,500 votes or 0.3 percentage points — the results were anything but close in most precincts across Cook County, according to a WBEZ analysis of election returns as of March 31.

Both O'Neill Burke and Harris won hundreds of precincts by wide margins of 20, 30 and even 50 percentage points or more, the analysis shows.

The margin of victory was at least 20 percentage points in more than 71% of the county’s 2,700 precincts, according to the analysis. The margin of victory was at least 40 percentage points in more than 42% of the county’s precincts.

Here’s a breakdown of some key findings from WBEZ’s analysis, which provides a glimpse into an election that could have gone either way.

Harris won big, but O’Neill Burke won more often

Harris captured nearly 400 precincts by 50 percentage points or more, compared to about 300 such precincts for O'Neill Burke. Harris was strongest in precincts on the South and West sides of Chicago and throughout the south suburbs and near west suburbs.

But O'Neill Burke captured nearly 460 more precincts than Harris overall. Her strongest showings came in precincts on the Northwest and Southwest sides of the city and near downtown. O'Neill Burke also scored big in the near northwest and near southwest suburbs. She carried more than twice as many precincts as Harris — 991 to 430 — in suburban Cook County.

Black voters overwhelmingly backed Harris, but turnout was low

Despite losing more precincts than he won, Harris remained competitive thanks to strong support from Black voters in the city and suburbs. Harris won nearly 77% of the combined vote in majority-Black precincts throughout the county. He amassed about 67,000 more votes than O'Neill Burke did in those precincts.

But that margin could have been much wider in those precincts if voters there had turned out in numbers similar to those seen in two previous Democratic primaries for state’s attorney. In 2016 and 2020, when Democratic primaries featured competitive presidential races at the top of the ballot, majority-Black precincts turned out far more voters than they did last month.

Majority-Black precincts countywide logged about 126,000 votes in last month’s Democratic primary for state’s attorney, a far cry from the 350,000 in 2016 and 230,000 in 2020. In those elections, majority-Black precincts were instrumental in State’s Attorney Kim Foxx’s victories.

While Harris enjoyed strong support in majority-Black precincts, he polled a few percentage points behind Foxx’s showings in those precincts in 2016 and 2020. And despite the low vote totals in majority-Black precincts, a few extra percentage points in his strongholds could have made a difference.

For instance, if Harris had won 83.5% of the vote in majority-Black precincts last month — as Foxx did in 2020 — it would’ve improved his overall vote total by about 9,000 votes, roughly six times more than the votes he needed to win.

O’Neill Burke wins most votes in white, Asian and Latino areas

Collectively, O'Neill Burke captured just 23% of the vote in majority-Black precincts in the county. However, she doesn’t believe her message didn’t resonate with voters on the city’s South and West sides.

“I think that people everywhere are concerned about violence and crime in their communities,” O'Neill Burke said. “I think it was a question of messaging. And we will work very, very hard throughout this next campaign season until November to make sure every single community in Cook County understands what my positions are on things and understands what my vision is for bringing the State’s Attorney’s Office forward.”

O'Neill Burke made up for her losses in majority-Black precincts with strong performances elsewhere. She won nearly 59% of the votes outside of majority-Black precincts. O'Neill Burke, whose campaign was powered by big donations from white men, captured more than 178,000 votes — about 70,000 more than Harris — in majority-white precincts across the county. She also captured nearly two-thirds of the vote in majority-Asian precincts, and narrowly edged Harris in majority-Latino precincts.

Some of her strongest support among majority-Latino precincts in the city came from the 10th, 13th and 23rd wards on the city’s Southwest and Southeast sides. In those precincts, she, collectively, captured about 68% of the vote.

“I can tell you that, in the Southwest Side by Midway, we came out strong for her. And we're going to continue to come out strong for her in November,” said Ald. Silvana Tabares, 23rd Ward. “Very proud, very happy, and I look forward to working with her.”

Alden Loury is the data projects editor for WBEZ. Reporter Michael Puente is on WBEZ’s Race, Class and Community team.