Dementia is a common and disabling brain disorder among older adults that has consequences for independence, functional decline, institutionalization, and mortality. Previous research has identified multiple biological, genetic, and behavioral factors that are associated with cognitive impairment and decline. For example, a relatively common polymorphism in the apolipoprotein E (ApoE) gene, the allele, is strongly associated with cognitive decline and is significantly higher among those with Alzheimer?s disease compared to rest of the population. Recently, a parallel literature has looked beyond individual-level factors to consider the role of the social and built environment. Findings suggest that residence in socioeconomically advantaged neighborhoods may promote cognitive function and/or buffer cognitive decline in part through their greater density of physical resources (recreational centers, gyms, parks, walking paths, healthy food stores) as well as social and institutional resources (libraries, bookstores, community centers, social clubs) that promote physical activity and facilitate mental stimulation (e.g. social interaction). However, an interesting question remains as to whether there are specific sub-populations of older adults who may especially benefit from residence in resource-intensive neighborhoods by virtue of the fact that they are at higher risk for cognitive decline because they carry the allele. We propose to conduct a secondary analysis of data from the Chicago Neighborhood and Disability Study, part of the Chicago Health and Aging Project, a prospective NIA-funded population based cohort study of older adults in the city of Chicago who were surveyed 7 times over a 13 year period (1993-2006). In addition to being a longitudinal study collecting genetic markers for dementia (APOE allele), the study also collected objectively measured, detailed environmental data (including sidewalk quality, parks, trees, public transit, benches, safety, libraries, churches, schools). As such, the data provide an ideal opportunity to examine the possible role of neighborhood environments in modifying cognitive decline among older adults who are genetically at risk.