Foxx said she couldn't justify spending the time and manpower to go to trial now that Kelly has been convicted twice on federal charges.
"Sometimes justice is served even when there is no conviction," Foxx said, adding that prosecutors will go to court Tuesday and ask a judge to drop the charges against Kelly.
In February 2019, Foxx filed 10 counts against Kelly for having sex with four underage girls and taping some of the encounters. The charges came in the wake of the documentary series, "Surviving R. Kelly."
After that series aired, Foxx pleaded with accusers to come forward so that prosecutors could pursue charges. She announced the Cook County indictment months before the federal cases in New York and Chicago. Foxx's office alleged he repeatedly sought out girls for sex, including one he encountered at her 16th birthday party and another who met him while he was on trial in 2008.
But now that Kelly has been convicted on similar charges by federal prosecutors in both Chicago and New York, Foxx said it no longer makes sense to put him on trial on state charges for the same crimes.
"Due to the extensive sentences that these convictions hold, our office has decided not to continue to expend our limited resources and court time with the indictments we previously charged Mr. Kelly," Foxx said.
Kelly is already serving a 30-year prison sentence for the federal case in New York and will likely receive a similar term when he's sentenced in Chicago next month.
Based on the New York sentence alone, the 56-year-old won't be eligible for release until he is around 80.
Another sexual-misconduct case is pending in Hennepin County, Minnesota, where the Grammy Award-winner faces solicitation charges. That case, too, has been on hold while the federal cases played out. Minnesota prosecutors haven't said whether they still intend to take Kelly to trial.
Foxx said she consulted with Kelly's victims before making Monday's announcement, and while one was disappointed she won't be able to face Kelly in court, Foxx said the others were relieved.
"For them, the process of going through this process was very difficult, and they are pleased with the outcome of the sentence and judgment against Mr. Kelly," Foxx said.
Chicago lawyer and legal analyst Karen Conti said it's also possible Foxx didn't want to risk endangering the federal convictions.
"It could be that if there's a jury verdict that is a loss in the state court, it could be used in the federal court appeal to show there are inconsistent verdicts, and that could imperil the verdict that happened in federal court," Conti said.
Kelly remains locked up at the metropolitan correctional center in the Loop, awaiting sentencing on the Chicago federal charges next month.
The Associated Press contributed to this report.