Introduction: Individuals with mental illness often experience stigma from healthcare professionals, including emergency nurses. The purpose of this study was to identify personal and professional attributes of emergency nurses that may be related to their level of stigma toward people with mental illness in the U.S. Methods: Secondary analysis of a cross-sectional study to analyze emergency nurses' characteristics against their perceptions of stigma toward mental illness as measured by the Mental Illness: Clinicians' Attitudes Scale-4 (MICA v4). Data analyses consisted of descriptive statistics; stepwise linear regression; and analysis of the internal consistency of the MICA v4 in the current sample. Results: The mean MICA v4 scores for this sample were 53.4. The linear regression analysis revealed a significant model explaining 23.5% of the variance of MICA v4 scores (F[34] = 6.4, p < 0.001, R2 = 0.235). Many attributes were found to have a strong association with lower stigmatizing attitudes. Discussion: The results of this study indicated high levels of stigma toward individuals with mental illness. Findings from this study can inform nursing education and research, and ultimately improve the health outcomes of individuals with mental illness.