Many older adults living with dementia have not been formally diagnosed. Even when clinicians document the diagnosis, patients and families may be unaware of the diagnosis. Knowledge of how individual characteristics affect detection and awareness of dementia is limited. To identify characteristics associated with dementia diagnosis and awareness of diagnosis. Cross-sectional observational study. Five hundred eighty-five adults aged ≥ 65 in the National Health and Aging Trends Study who met assessment-based study criteria for probable dementia in 2011 and had 3 years of continuous, fee-for-service Medicare claims prior to 2011. Using multivariable logistic regression, we compared participants with undiagnosed versus diagnosed dementia (based on Medicare claims) on demographic, social/behavioral, functional, medical, and healthcare utilization characteristics. Among those diagnosed, we compared characteristics of participants unaware versus aware of the diagnosis (based on self or proxy report). Among older adults with probable dementia, 58.7% were either undiagnosed (39.5%) or unaware of the diagnosis (19.2%). In adjusted analyses, individuals who were Hispanic (OR 2.48, 95% CI 1.19, 5.14), had less than high school education (OR 0.54 for at least high school education, 95% CI 0.32, 0.91), attended medical visits alone (OR 1.98, 95% CI 1.11, 3.51), or had fewer functional impairments (OR 0.79 for each impairment, 95% CI 0.69, 0.90) were more likely to be undiagnosed. Similarly, among those diagnosed, having less education (OR 0.42), attending medical visits alone (OR 1.97), and fewer functional impairments (OR 0.72) were associated with unawareness of diagnosis (all ps < 0.05). The majority of older adults with dementia are either undiagnosed or unaware of the diagnosis, suggesting shortcomings in detection and communication of dementia. Individuals who may benefit from targeted screening include racial/ethnic minorities and persons who have lower educational attainment, any functional impairment, or attend medical visits alone.