Joseph Czuba of Plainfield was sentenced earlier this year for stabbing 6-year-old Wadee Alfayoumi to death.
The 73-year-old died on Thursday, according to the Will County Sheriff's Office.
In October 2023, Alfayoumi died after police said Czuba stabbed him more than 24 times.
He also seriously injured Alfayoumi's mother, who was stabbed at least a dozen times.
Prosecutors said Czuba called the boy's mother a "devil Muslim," while he stabbed them in the home they were renting from him.
A jury convicted him in February on charges of first-degree murder, attempted murder and hate crimes.
In May, he was sentenced to 53 years in prison.
Czuba's cause of death was not released.
CAIR Chicago's Executive Director Ahmed Rehab said in a statement: "This depraved killer has died, but the hate is still alive and well. Wadee was stabbed to death 26 times for being Palestinian. Two years later, even as we speak, thousands of Gazan children are being shot, bombed and starved to death for being Palestinian. It's the hate that must die."
MORE ON THE CASE | Joseph Czuba sentenced to 53 years in prison in Will County hate crime stabbing of Muslim boy