Background: About one in five adults in the United States experience any mental illness (AMI), whereas 14.2 million experience serious mental illness (SMI). The perception of stigma among individuals experiencing mental illness is associated with care seeking behavior and treatment adherence. Purpose: Two factors that mitigate stigma are familiarity with someone experiencing AMI/SMI and general level of education. Heretofore, these factors have not been tested together to determine if familiarity moderates the relation between level of education and stigma of professional efficacy for treating mental illness. Methods: In fall 2020, an online survey in the state of Utah measured 1,300 adults' perceptions of stigma for AMI/SMI using a validated instrument. Data were analyzed using logistic regression. Results: Results indicate that familiarity (i.e. self or immediate family member versus other person) moderated level of education for stigma of professional efficacy for treatment of AMI but not SMI. Discussion: Participants viewed the professional efficacy of treating AMI and SMI differently. These findings have implications for educational interventions designed to mitigate public stigma for professional efficacy of treating mental illness. Translation to Health Education Practice: Emphasizes the National Commission for Health Education Credentialing Inc. assessment of needs and capacity, and evaluation and research competencies. A AJHE Self-Study quiz is online for this article via the SHAPE America Online Institute (SAOI) http://portal.shapeamerica.org/trn-Webinars.