The fire broke out at about 3 a.m. at AAA Galvanizing on Mills Road. Flames raced through the building, which is approximately one block long and one block wide.
The East Joliet deputy fire chief calls it one of the largest fires in his career.
Crews were expected to stay on scene most of Sunday to get the fire under control.
No one was hurt.
The cause of the fire is under investigation.
