Randy Hancock, 50, died in the burn unit at a Springfield hospital, Sangamon County Coroner Susan Boone said.
He was the fifth employee at the Formosa Plastics plant to die from injuries suffered in the April 23 explosion, Boone said. An autopsy showed that Hancock died from complications related to the severe burns that covered 60 percent of his body.
His wife, 56-year-old Linda Hancock, was among the four workers whose bodies were recovered from the Illiopolis plant after the explosion.
Employees were mixing vinyl chloride and vinyl acetate when the blast happened, destroying much of the plant and igniting a fire that burned for more than two days.
Illiopolis' 1,000 residents were evacuated after the explosion because of the hazardous fumes. The city is about 20 miles east of Springfield.