Firefighters were called to Del Real Stables in the 1100 block of Wheeler Road around 1:15 a.m., Plainfield Deputy Fire Chief Jon Stratton said.
When they arrived, the west side of a barn was fully engulfed by flames. The fire spread before crews were able to get it under control around 1:45 a.m., Stratton said.
The owner of the stable put out an alert on Facebook asking people to help find 19 missing horses that were let out during the fire. By around 7:30 a.m., he said all of the horses had been accounted for.
Thirty horses were in the barn when the blaze broke out, and 18 of them died.
Two horse owners sustained minor injuries. It is unclear whether they were inside the barn when the fire started.
Nearly seven hours later, crews were still dousing hot spots. The barn was destroyed.
The cause of the fire was under investigation.