Authorities say deputy chief of staff Carla Oglesby is charged with three felonies and is being held on $75,000 bond.
Oglesby had no comment as police brought her to Area 4 headquarters Monday night.
A spokesperson for Todd Stroger's office declined to comment, saying they need to learn more about the charges.
"A weapon wasn't used, it was a pen. Here is the kind of financial abuse that we have to be subjected to by people who are enjoying or should be, you know, practicing public trust. And instead they're stealing money and diverting it to inappropriate and illegal uses to reward Stroger campaign workers," said Comissioner Tony Peraica.
The charges include three felonies: theft of government property, money laundering and official misconduct. They apparently stem from a series of no-bid contract Oglesby awarded to a number of friends and allies, including her own public relations firm, all at just under the $25,000 mark that would require approval from the full county board.
In an interview several months ago, Oglesby told ABC7's Ben Bradley she's done nothing wrong.
"You certainly can be working on a campaign or for any other client and working for the county on a project at the same time. There's absolutely nothing wrong with that. There's certainly nothing illegal about that," she said.
County commissioners have since voted to change the rules on no-bid contracts, but several commissioners say they believe the investigation is far from over.
"The fact that President Stroger put her in a position to award contracts to her own firm and there were no systems to catch that, no audits or procedures, is very troubling," said Commissioner Forrest Claypool.
"I think there's culpability going all the way up to Todd Stroger because he was the one who signed these contracts and of course his signature is on the checks," said Peraica.
Oglesby is scheduled to appear in bond court Tuesday morning. Cook County state's attorney Anita Alvarez has scheduled a news conference shortly after that appearance.