Previous research has shown strong positive associations between physical and psychological health outcomes and being in a committed relationship, such as marriage; however, little research has investigated whether being in a committed relationship is protective for day-to-day health behaviors such as dietary patterns and physical activity. This research examined associations between relationship status and day-to-day health behaviors (e.g., dietary intake, physical activity) and weight status among a diverse cohort of young adults. This cross-sectional study used data from Project EAT-III, a 10-year longitudinal population-based study (N = 1,853) of Midwest young adults. Young adult participants had an average age of 25.3 years, and were 45% male and 55% female. Participants were socioeconomically and racially/ethnically diverse, including 48.4% White, 18.6% African American, 5.9% Hispanic, 19.6% Asian, 3.3% Native American, and 4.2% mixed or other race/ethnicity. Results indicated that married men were more likely to be overweight/obese (body mass index ≥ 25) compared with single/casually dating and committed dating/engaged men. Married women were more likely to eat breakfast ≥5 times per week compared with women in other relationship categories. No differences were observed in other health behaviors by relationship status. There were no significant interactions by race/ethnicity. Relationship status seems largely unrelated to young adults' participation in physical activity and dietary behaviors. However, findings suggest that being married may be a risk factor for overweight/obesity in young adult men and may be a protective factor for health-related behaviors associated with overweight/obesity such as breakfast intake for young adult women.