Investigators were trying to find out how the two-alarm fire started around 9 p.m.
When crews arrived at 809 E. Park Ave., the two-story building was already evacuated. Firefighters saw smoke, elevated the response and began searching for the fire inside the building, the firefighter said.
"A bunch of pallets" and storage materials were found burning in the middle of the structure, according to the firefighter.
Crews extinguished the fire by 9:30 p.m., but it took until 1 a.m. to ventilate the smoky building and make sure the blaze was not burning anywhere else inside, the firefighter said.
One firefighter said the building was properly equipped with alarms and sprinklers that activated and helped douse the flames.
The structure, which is regularly rented out to several different companies to use for storage, did not sustain any damage, according to the firefighter, who did not know what caused the fire.
About 35 firefighters, including those who assisted Libertyville from Mundelein, Countryside, Long Grove, Deerfield and Lake Villa helped put out the fire.
The STNG Wire contributed to this report.