Evidence on cash transfers as a population-level intervention to support healthy cognitive aging in low-income settings is sparse. We assessed the effect of a cash transfer interven-tion on cognitive aging outcomes in older South African adults. We leveraged the overlaping the sampling frames of a Phase 3 randomized cash transfer trial [HIV PreventionTrial Network (HPTN) 068, 2011–2015] and an aging cohort [Health and Aging inAfrica: A Longitudinal Study of an INDEPTH Community (HAALSI), 2014– 2022] in rural Mpumalanga Province, South Africa. In 2011/12, young women and their primary caregivers were randomly assigned 1:1 to receive a monthly cash transfer orcontrol. In 2014/2015, 862 adults aged 40+ y living in trial households were enrolled inthe HAALSI cohort, with cognitive data collected in three waves over 7 y. We estimatedthe impact of the intervention on rate of memory decline and dementia probability scores. Memory decline in the cash transfer arm was 0.03 SD units (95% CI: 0.002,0.05) slower per year than in the control arm. Dementia probability scores were three percentage points lower in the cash transfer arm than the control arm (β = −0.03; 95%CI: −0.05, −0.001). Effects were consistent across subgroups. A modestly sized house-hold cash transfer delivered over a short period in mid- to later-life led to a meaningfulslowing of memory decline and reduction in dementia probability 7 y later. Cash transferprograms could help stem the tide of new dementia cases in economically vulnerablepopulations in the coming decades.