The association of atrial fibrillation (AF) with cognitive function remains unclear, especially among racially/geographically diverse populations. This analysis included 25,980 black and white adults, aged 48+, from the national REasons for Geographic and Racial Differences in Stroke (REGARDS) cohort, free from cognitive impairment and stroke at baseline. Baseline AF was identified by self-reported medical history or electrocardiogram (ECG). Cognitive testing was conducted yearly with the Six Item Screener (SIS) to define impairment and at 2-year intervals to assess decline on: animal naming and letter fluency, Montreal Cognitive Assessment (MoCA), Word List Learning (WLL) and Delayed Recall tasks (WLD). Multivariable regression models estimated the relationships between AF and baseline impairment and time to cognitive impairment. Models were adjusted sequentially for age, sex, race, geographic region, and education, then cardiovascular risk factors and finally incident stroke. AF was present in 2,168 (8.3%) participants at baseline. AF was associated with poorer baseline performance on measures of: semantic fluency (p<0.01); global cognitive performance (MoCA, p<0.01); and WLD (p<0.01). During a mean follow-up of 8.06 years, steeper declines in list learning were observed among participants with AF (p<0.03) which remained significant after adjusting for cardiovascular risk factors (p<0.04) and incident stroke (p<0.03). Effect modification by race, sex and incident stroke on AF and cognitive decline were also detected. In conclusion, AF was associated with poorer baseline cognitive performance across multiple domains and incident cognitive impairment in this bi-racial cohort. Additional adjustment for cardiovascular risk factors attenuated these relations with the exception of learning.