A bomb threat caused a Purina Plant in Clermont County to evacuate on Monday.According to the Clermont County Sheriff's Office, an employee at the plant called the county's call center around 9:12 a.m., saying a note that had today's date had been discovered at the plant that indicated there was a "bomb inside."The plant's management team told employees to leave for the day after getting word about the note. The sheriff's office, along with the Williamsburg Township Fire Department, responded to the plant, located on Afton Drive, and evacuated the facility so they can do a thorough search.Special K9 units trained in detecting explosive devices were called in from nearby agencies including the Miami Township Police, University of Cincinnati police, Northern Kentucky University and the Hamilton County Sheriff's Office.The units arrived less than an hour after the call was made and searched the area and inside the business.No items or devices were found, the sheriff's office said.Detectives with the sheriff's office determined the message that was found inside a Porta Potty on the property, that was hidden from surveillance cameras.The sheriff's office said nearly 900 employees were onsite when the incident happened.The source of the threatening note remains unknown but detectives are investigating all potential leaders.Anyone with information is asked to call the Clermont County Sheriff's Office.