Video from the incident showed the blast lit up the night sky on Friday in Waukegan, a community 40 miles (65 km) north of downtown Chicago.
Nine employees were in the building at the time of the blast, and four have been hospitalized while two others did not require treatment.
Local media reports identified the plant as AB Specialty Silicones.
The 30,000-square foot (2,800 square meters) plant operated around the clock, and most of the chemicals on site were used to produce silicone.
Images of the plant from local media showed its walls stripped away, leaving only a shell of a building with girders and scraps of roofing material.
The cause of the explosion and fire was under investigation.
(Production: Kia Johnson)