Background African American adults experience a disproportionate burden of dementia, shaped by structural and clinical factors that remain unclear. Objective To quantify associations between multimorbidity, polypharmacy, and cognition in the context of neighborhood disadvantage. Methods This study is a cross-sectional analysis of 348 African American adults aged 45–92 years (mean 64.3 years; 73.6% female) from the Aging Research Characterizing Health Exposome via Social drivers (ARCHES) cohort. Comorbidity burden was assessed using a modified Charlson Comorbidity Index (CCI), polypharmacy as ≥5 medications, and neighborhood disadvantage using the Area Deprivation Index (ADI). Linear regression estimated associations with a Preclinical Alzheimer’s Cognitive Composite (PACC). The polypharmacy model included modified CCI as a covariate, and effect modification by ADI was assessed using an interaction term between polypharmacy and ADI. Results Higher modified CCI was associated with lower cognitive performance (B = −0.071; 95% CI: −0.130, −0.012). Polypharmacy was not independently associated with cognition after modified CCI adjustment (B = −0.081; β = −0.057; p = 0.257). No significant ADI interaction was found (p = 0.064).