AbstractINTRODUCTIONThe fraction of dementia attributable to hypertension might vary depending on the age of the population considered and the age through which dementia occurs.METHODSIn the Atherosclerosis Risk in Communities study, we quantified population attributable fractions (PAF) of dementia by age 80 and 90 from hypertension assessed at ages of 45–54 (n = 7572), 55–64 (n = 12,033), 65–74 (n = 6561), and 75–84 (n = 2086).RESULTSThe PAF for dementia by age 80 from all non‐normal blood pressure at ages 45–54 was 15.3% (95% confidence interval [CI] = 6.9%–22.3%), 19.1% (95% CI = 9.9%–26.9%) at ages 55–64, and 19.9% (95% CI = −4.4%–38.5%) at ages 65–74. The strongest PAFs were from stage 2 hypertension (11.9%–21.3%). For dementia by age 90, PAFs from non‐normal blood pressure up through age 75 were smaller (10.9%–13.8%), and non‐significant by age 75–84.DISCUSSIONInterventions targeting hypertension even in early late life might reduce a sizeable proportion of dementia.Highlights We estimated prospective population attributable risks of dementia for hypertension. 15%–20% of dementia cases by age 80 are from non‐normal blood pressure (BP). Associations between hypertension and dementia persisted through age 75. Midlife to early late‐life BP control might reduce a large proportion of dementia.