Objectives: To examine the prevalence of Post-Traumatic Stress Disorder (PTSD) in a sample of prison employees, investigate risk factors, and explore protective factors for PTSD. Methods: We surveyed 355 Washington State Department of Corrections employees. The survey included the PTSD checklist for the DSM-5 (PCL-5), the Critical Incident History Questionnaire, and the Work Environment Inventory. Results: We found 19% of the sample met the criteria for diagnosable PTSD. Several risk factors were associated with a higher PCL-5 score, including exposure to critical incidents, and having greater ambiguity in the job role. Being happy with job assignments and having positive relationships with supervisors and coworkers were associated with decreased PCL-5 score. Conclusions: Prison employees have a PTSD rate equivalent to Iraq and Afghanistan war veterans and higher than police officers, suggesting the importance of developing programs for promoting resilience to stress, incorporating the knowledge gained on risk, and protective factors.