This project will produce and disseminate a publicly available dataset of net migration estimates for all US counties by five-year age group, sex, race, and Hispanic origin for the 2010-2020 decade. In addition, the project will provide access to these data for a broad community of researchers and practitioners in demography and population health through an interactive website for on-line mapping, analysis, and data downloads. The 2010-2020 estimates will be integrated with similar net migration estimates produced each decade since 1950 to generate a longitudinal dataset of 70 years of age-specific net migration for all US counties. The project will derive estimates using a forward cohort residual method, subtracting a measure of natural increase from population change over the period to generate net migrants. Estimates will be highly accurate and reliable. We will produce them by using high quality data that avoid sampling error, including enumerations from Census 2010 and 2020 and administrative records of all US births and deaths from the National Center for Health Statistics. These estimates will be critically important for research on a variety of population and population health policy-relevant topics at the crux of which is migration patterns and trends: migration of the baby boom cohort and its impact on health care demand at destination; race-specific migration patterns and subsequent health disparities for populations of color; the persistence of high out-migration regions and its contribution to shrinking economies; and young adult out-migration and its impact on the health of the population that remain (i.e., mental health, health behaviors, life expectancy). Age-specific migration’s spatial distribution influences the age structure of communities, with significant implications for population aging, child health, education, and economic well-being. Selective migration by age, sex, and race/ethnicity alters counties’ population composition, having significant implications for health service provisioning and staffing, service infrastructure development, economic and labor market conditions, fertility, and mortality. Accurate net migration estimates by detailed demographic characteristics are essential for research analyzing place-based age- specific migration patterns and their relationship with health factors and outcomes, and for practitioners planning for public health services, civic infrastructure, and community and economic development. The proposed set of county-level net migration estimates are vital to applied demographers making small area population estimates and projections, which are the basis of health service planning efforts. Without the proposed data, there will be no age- or race/ethnic-specific county-level migration estimates for the post 2010 period for all US counties. The team will make the data available and accessible to planners, healthcare administrators, health policy-makers, and other decision-makers and ...