Differences in mental illness (MI) stigma among adolescents were examined cross-sectionally across race, ethnicity, and gender to identify target populations and cultural considerations for future antistigma efforts. An ethnically and socioeconomically diverse sample of sixth graders (N = 667; mean age = 11.5) self-completed assessments of their MI-related knowledge, positive attitudes, and behaviors toward peers with MI and adolescent vignettes described as experiencing bipolar (Julia) and social anxiety (David) symptoms. Self-reported race, ethnicity, and gender were combined to generate 6 intersectional composite variables: Latino boys, Latina girls, non-Latina/o (NL) Black boys, NL-Black girls, NL-White boys, and NL-White girls—referent. Linear regression models adjusting for personal and family factors examined differences in stigma using separate and composite race, ethnicity, and gender variables. In main effects models, boys and Latina/o adolescents reported greater stigma for some outcomes than girls and NL-White adolescents, respectively. However, intersectional analyses revealed unique patterns. NL-Black boys reported less knowledge/positive attitudes than NL-Black and White girls. NL-Black and Latino boys reported greater avoidance/discomfort than NL-White girls. Moreover, NL-Black girls and boys and Latina/o girls and boys wanted more social separation from peers with mental illness than NL-White girls; NL-Black boys also reported more separation than NL-White boys, NL-Black girls, and Latina girls. Finally, NL-Black boys and Latina girls wanted more distance from David than NL-White and Black girls. Vital for informing future antistigma interventions, this study generates new knowledge about how differences in views about MI exist across racial and ethnic identity, and how gender intersects with these perceptions.