PROJECT SUMMARY The parent grant (R01AG074359) specific aims are to estimate the effects of early-life social and environmental exposures on late-life cognitive health (Aim 1-2), estimate their synergistic effects (Aim 3), and evaluate the extent to which the early-life factors modify the effects of APOE-e4 on late-life cognitive health (Aim 4). To complete all four aims, we have a methodological goal to estimate 1940 social and environmental exposures at the community level for Health and Retirement Study (HRS) participants. This involves using 1940 US Census data at the enumeration district level and numerous measures of environmental exposures at different spatial resolutions, including traffic-related air pollution, fine particulate matter, power plant exposure, and oil and gas well exposure. Currently, HRS has information on the enumeration districts where participants lived in 1940. This information is supplied with the enumeration district code. However, the spatial locations of the enumeration districts are not currently available. In order to link our social and environmental exposures to HRS participant locations, we require digitized and georeferenced information on enumeration district locations and boundaries across the US in 1940. The maps necessary to provide this information are available in paper format at the National Archives in College Park, MD. This proposal will allow us to digitize county or city-level 1940 Census enumeration district maps containing 1940 residences of HRS participants and then georeference the enumeration districts with HRS participants. We will also use previously digitized and georeferenced information from 53 cities as part of the Urban Transition Project. Final output from this proposal will consist of a spatial data frame containing enumeration district identifiers, centroid latitude and longitude, and the enumeration district polygon. We will document our methods and share the spatial data files with the HRS team to make them available to other HRS restricted data users. The dataset will be foundational in the parent R01, allowing us to link a host of social and environmental data to participant residential locations in 1940. Analyses using this dataset have the potential to uncover new early-life predictors of Alzheimer’s disease and related dementias (AD/ADRD) and cognitive decline.