In this study, we examined ethno-racial differences in daily functioning in 66 non-Latinx White participants, 83 non-Latinx Black participants, and 60 Latinx participants (N = 209) diagnosed with serious mental illnesses, and the extent to which individual socioeconomic status (SES), neighborhood SES, and symptom severity accounted for observed differences. Participants completed ecological momentary assessments of what they were doing, who they were with, and where they were three times daily for 30 days. Black participants more frequently reported being alone or engaged in passive leisure (e.g., watching TV) than White participants and Latinx participants, less frequently reported vocational activity than Latinx participants, and less frequently reported home-based active leisure than White participants. Although some findings were accounted for by neighborhood SES, individual SES, or symptoms, there is also a need to explore sociocultural and racism-related explanatory factors. Clinical implications (e.g., providing vocational services to Black clients) and future research directions are discussed.