Spiros Elias of Burlington was arrested last Friday and charged with first degree murder.
Aurora police said the charges stemmed from a case that began on Dec. 17, 2010 in the 100-block of Cross Street.
An 11-month-old boy named Michael Ortiz was found unconscious and not breathing.
He was hospitalized and died the next day, police said.
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The DuPage County Coroner's Office said the child's death was caused by injuries resulting from child abuse and classified his death as a homicide.
"Despite a thorough investigation, the initial investigators were unable to determine who was responsible, and the case remained unresolved," Aurora police said.
In December 2024, the Aurora police cold case investigator looked back into the case.
Through more investigation, police determined Elias, Ortiz's mother's live-in boyfriend at the time, was allegedly responsible for the boy's death.
Elias appeared for a pretrial detention hearing Friday, where he was ordered held in the Kane County Jail.
He is next due in court Oct. 15.
"A child's life was taken, and Michael's family has lived for more than 15 years without answers or accountability," Aurora Police Chief Matt Thomas said. "While this arrest cannot undo their loss or erase the pain caused by the passage of time, we hope it brings them one step closer to justice. Cold cases are never forgotten, and we will continue pursuing justice no matter how much time has passed. I am proud of the dedication, persistence, and specialized investigative work that brought this case to this point."