As the number of older adults continues to increase, so will the number of cases of dementia. Timely diagnosis ensures these patients and their caregivers receive appropriate treatment and support. This study utilized five longitudinal research cohorts to estimate timely diagnosis of clinical dementia, defined as a clinical diagnosis 3 years before or 1 year after the date of cohort evaluation at which a participant’s symptom of dementia was noted for the first time. Only half of older adults with incident dementia diagnosed within the research study received a timely clinical diagnosis of dementia. Black older adults and those with lower income, higher baseline cognitive functioning, and fewer comorbidities were at increased risk of delayed diagnosis.