Dementia prevalence exceeds 40% for individuals in advanced old age, but that figure is not informative about the lifetime risk of ever having dementia or the risk of having dementia for different durations. This study presents U.S. nationally representative estimates of the probability of having dementia for at least six months or one, two, or five years before death and variation in this probability by sex, race and ethnicity, health, and socioeconomic status. We used a joint longitudinal latent variable model of cognitive status, dementia, and survival to derive estimates based on data from the Health and Retirement Study. We found a higher lifetime risk of dementia than found in earlier U.S. studies: 41.3% (CI: 39.3% to 43.2%) of those who died after age 70 had dementia assessed at six months before death. Further, 38.7% (CI: 36.8% to 40.5%), 33.6% (CI: 31.8% to 35.4%), and 20.1% (CI: 18.6% to 21.5%) had dementia one, two, and five years before death, respectively. The risk was higher for women, individuals with less education, non-Hispanic Black individuals, and those with lower lifetime earnings. Having had a stroke significantly increased the risk of dementia. Even though longevity is the strongest known risk factor, longer lived subpopulations have a lower lifetime risk of dementia as a result of their lower age-specific prevalence.