As of 10:45 a.m., the individual was in custody, police said. No details about the person were immediately provided.
Early Thursday morning, police said they had released a second person of interest without charges in the death of Stacey Jones, a 35-year-old Cook County probation officer who was found unresponsive on the porch of her home in the 2100-block of East 95th Place just after midnight Oct. 13.
Chicago police said last week that another suspect in Jones' death was released without charges.
Jones, a mother of two, was eight months pregnant at the time of her death. Police said she was found with two gunshot wounds.
Jones was rushed to the University of Chicago hospital in critical condition, where she later died, police said.
Doctors were able to deliver her baby, who remained in critical condition until his death Saturday at University of Chicago Medical Center.
The baby boy was just four days old when he died, according to the Cook County Medical Examiner's Office.
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Police said they are focusing their investigation on people who were known to the mother of three.
Neighbors said Jones, who is originally from Tennessee, had lived at the address of the shooting for less than a year. They last saw Jones playing outside with her other two young children in early October.
"I just saw her Friday, and she was telling me how happy she was that she was about to have a baby," said Nicholas Minor, a friend and coworker. "Stacey was a very perky person, you know, always had a smile every morning coming to work. Every day, every time I saw her she'd say, 'Hi Nick!'"
Minor said her job was her passion, but Jones' pride was her children. He said her murder not only stole her future, but robbed her boys of a loving mother.
Area Two detectives are investigating the shooting.
They said police found racially-tinged graffiti on the side of Jones' apartment, but believe it was placed there as a diversion.
Anyone with information is asked to call CPD or text 274637 to submit a tip anonymously.