Correctional workers are regularly exposed to potentially psychologically traumatic events, which are associated with mental health disorders. Correctional workers report barriers to mental health service use due to difficulties recognizing mental health needs and stigma, leading to compromised mental health. The current study was designed to assess nuances in mental health knowledge, stigma, and service use intentions among correctional workers and differences based on demographic categories and histories of mental health disorders. Participants (n = 878) were correctional workers from Ontario, Canada, who completed the Mental Health Knowledge Scale, the Opening Minds Scale for Workplace Attitudes, and the Mental Health Service Use Questionnaire. There were statistically significant differences on measures of mental health knowledge, stigma, and service use intentions across most demographic categories. There were statistically significant differences on a measure of mental health service use intentions between participants with and without a history of mental health disorders. Mental health knowledge contributed significantly to the variation in service use intentions. The current results provide initial baseline data for correctional workers regarding mental health knowledge, stigma, and service use intentions. The results evidence demographic differences that may help focus training efforts. The results also suggest experiencing mental health disorders may be insufficient to overcome mental health stigma, which means additional individual, organizational, and structural efforts are warranted to increase service use intentions among correctional workers as part of supporting better mental health.