OBJECTIVES: Drawing from life course and environmental perspectives, we examined the trajectory of cognitive function and how senior housing moderates the effects of life-course socioeconomic status (SES) disadvantage among older people living alone over time. METHOD: Six waves of the Health and Retirement Study (HRS) were used with multilevel growth modeling to analyze developmental patterns of cognitive function over time and how various forms of life-course SES disadvantage affect cognitive function depending on senior housing residency status. RESULTS: At baseline, we found a positive role of senior housing in four subgroups: SES disadvantage in childhood only, unstable mobility pattern (disadvantage in childhood and old age only), downward mobility (no disadvantage in childhood, but in later two life stages), and cumulative disadvantage (all three life stages). Over time, the positive role of senior housing for the unstable and the most vulnerable group persisted. DISCUSSION: Our findings provide a much-needed practical and theoretical underpinning for environmental policy-making efforts regarding vulnerable elders who live alone.