The Cook County Regular Democratic Organization will hold its annual fundraiser on Thursday and use the occasion to honor an unpopular political figure: ex-party chairman and departing Cook County Assessor Joe Berrios.

On Wednesday, mayoral candidate Lori Lightfoot used the party’s decision to honor Berrios to lambast his successor as party chairman, County Board President Toni Preckwinkle, who’s also running for mayor.

Lightfoot branded Berrios the “poster child for bad government” for padding his payroll with relatives and “refusing to abide by any ethical standards,” in part, by thumbing his nose at the authority of the county’s inspector general and Ethics Board and fighting their restrictions at taxpayers’ expense.

She further accused Berrios of presiding over a flawed and unfair property assessment system that has favored the wealthy and politically-connected, at the expense of the average homeowner and the working poor.

The fact that Preckwinkle endorsed Berrios over Democratic primary winner Fritz Kaegi and leads a Democratic party that chose to honor him shows how “out of step” she is with everyday voters, Lightfoot said.

“To laud his efforts in the face of that clearly documented history of ethical misconduct and harm to low-income and working class families . . . shows a tone-deafness to the voters of this city. It says she’s not listening and doesn’t represent the kind of change Chicago needs,” Lightfoot said.

“Toni Preckwinkle is endorsing this honoring of Joe Berrios. She has stood up for him repeatedly in the face of overwhelming evidence . . . This kind of machine-style, we’ll-do-whatever-we-want, the-voters-be-damned attitude is not gonna be tolerated by the voters of this city.”

By leveling her first political broadside at Preckwinkle, Lightfoot is serving notice she has no intention of dropping out of the crowded race to replace Mayor Rahm Emanuel.

Monica Trevino, a spokesperson for Preckwinkle’s mayoral campaign, refused to comment on the political broadside from Lightfoot.

Berrios could not be immediately reached for comment. He has previously defended the job he’s done as assessor.

Jacob Kaplan, executive director of the Cook County Regular Democratic Organization, made no apologies for the decision to honor Berrios, which was made by the party’s executive board.

“During his time here, the party endorsed many more minority candidates, women candidates. His record at the party level speaks for itself in terms of what he did to open up the party to more diversity and things like that. That’s the reason he’s being honored,” Kaplan said.

Asked about the assessment controversy, Kaplan said, “This is just about the party. It’s about his party leadership.”

Retired Chicago Teachers Union President Karen Lewis and retired Illinois Supreme Court Justice Charles Freeman will be honored along with Berrios at the Thursday night fundraiser at the Chicago Hilton and Towers, Kaplan said.

Although Lightfoot used the Berrios honor to hammer Preckwinkle, it was vanquished Democratic gubernatorial challenger Chris Kennedy who got the ball rolling.

In a sharply-worded post on his Facebook page this week, Kennedy branded as “offensive” the decision to honor someone he called “a career politician who has run a corrupt assessor’s office.”

“In March, the voters firmly rejected Joe Berrios’ leadership . . . Just as voters didn’t honor him with elected office, so, too, should the Cook County Democratic Party refuse to honor him with tribute and recognition,” wrote Kennedy, who was endorsed by Lightfoot.

Mayoral candidate Bill Daley served as Kennedy’s finance chairman.

Kennedy argued that the party’s continued support of Berrios and “complicity in the corruption he represents” shows “more loyalty to elected officials” than the people the party purports to represent.

“The leadership in Cook County needs to catch up with the standards that Democratic voters of Cook County have established for their leadership. If they do not, they too, should be replaced, just as Joe Berrios was,” Kennedy wrote.

A Chicago Tribune investigation — and studies from respected sources, including the University of Chicago’s Center for Municipal Finance — have documented how the assessor’s office has massively undertaxed the most valuable homes in Chicago, shifting the cost to everybody else’s homes.

That has allowed clout-heavy attorneys who are among Berrios’ closest political allies, including House Speaker Michael Madigan (D-Chicago) and Ald. Edward Burke (14th), to successfully appeal assessment increases for their wealthy clients at the expense of the average Joe.