According to CNN, Waukegan Fire Marshal Steven Lenzi confirmed that everyone affected was an employee working at the time.
Four people, all employees, were transported to area hospitals with moderate to serious injuries.
The fire marshal said Saturday morning that in order to recover the other bodies, fire crews would have to wait until the remaining structure is torn down.
Crews at one stage have suspended their search for the other two workers due to concerns about the stability of the structure.
It wasn't immediately clear what caused the explosion, which damaged at least five other buildings in the area.
"I live in Antioch, 17.1 miles away and it shook my entire house", wrote one person on social media.
The explosion was heard and felt across the county, which is halfway between Chicago and Milwaukee, Wis.
"I along with the staff from the Lake County Sheriff's Office are very hopeful the three missing workers at the chemical plant are located alive, and all of those injured have fast recovery".
Authorities said the explosion damaged 90 percent of the plant, causing severe structural damage that is estimated to cost more than $1 million.
'Many neighboring properties are going to have damage, ' he said.
Florip said he would "categorize this as a massive explosion".
'Again, please stay out of the area and let the first-responders work'.
"The conditions are really rough in there", Lenzi said in the hours after the explosion.
Fire officials said that the air quality in the area is safe and there is no harm to residents. "We have had no instances as far as code violations or anything like that with the plant".