OBJECTIVE: One critical component of individual and public health is healthcare utilization, or the extent to which individuals have routine check-ups, schedule treatments, or use emergency services. However, we know little about who uses healthcare services and what types, the conditions that exacerbate utilization, or the factors that explain why people seek out services. The present study fills these gaps in the literature by investigating the role of personality factors in predicting various forms of healthcare utilization, how these associations vary by age, socioeconomic resources, and chronic conditions, as well as one potential psychological mediating mechanism (i.e., sense of control). METHODS: We use data from a large longitudinal sample of Americans (N = 7108), with three assessments spanning 20 years. Participants reported on their Big Five personality traits using the Midlife Development Inventory, healthcare utilization across three domains (routine visits, scheduled treatment, urgent care), age, income, insurance, chronic conditions, and sense of control. RESULTS: Multilevel models showed that people who were more agreeable and neurotic tended to use more healthcare services. Moreover, on occasions when people were more extraverted and open, they tended to use more healthcare services. There were several nuances in personality-healthcare utilization associations depending on the type of healthcare service, age, and socioeconomic resources. Longitudinal mediation analyses demonstrated sense of control as one mechanism linking personality traits to healthcare utilization in the U.S. CONCLUSIONS: We discuss the theoretical and practical implications of interactions between individuals and structural systems for promoting the health of aging U.S. Americans.