Background: Approximately 77% of older adults with dementia in Brazil have not been diagnosed, indicating a major public health issue. Previous epidemiological dementia studies in Brazil were based on data from 1 geopolitical region. Methods: We aimed to estimate the general and subgroup-specific (age, education, and sex) prevalence of dementia and cognitive impairment no dementia (CIND) classification using data from 5 249 participants aged 60 years and older from the ELSI-Brazil, a large nationally representative sample. Participants were classified as having normal cognitive function, CIND, or dementia based on a combination of the individual's cognitive and functional status. Results: We found a general prevalence of 5.8% (95% CI = 4.7-7.2) for dementia and 8.1% (95% CI = 6.8-9.5) for CIND. Dementia prevalence ranged from 3.2% (60-64 years old) to 42.8% (≥90 years old) by age, and from 2.1% (college level or higher) to 16.5% (illiterates) by education. Females had a higher dementia prevalence (6.8%) than males (4.6%). CIND prevalence was similar across age, sex, and education. Conclusions: The estimated dementia prevalence is lower than that in previous Brazilian epidemiological studies, but is in line with other Latin American studies. Only 1.2% of the ELSI-Brazil participants reported having a previous diagnosis of dementia, revealing that underdiagnosis is rampant and a common reality. Based on our results and national statistics projections, we estimate that in 2019, there were 1 757 480 people aged 60 years and older living with dementia in Brazil and, at least, another 2 271 314 having to deal with some form of cognitive impairment.