Research on health and mortality among adolescents and young adults in the United States lags behind comparable work on infants and older adults. A key limitation has been the lack of longitudinal, population-wide data linking healthcare access and utilization, demographic and socioeconomic characteristics, family context, and mortality outcomes. We construct YouthLink, a new prototype individual-level integrated database, by linking multiple administrative record sources within the secure environment of the U.S. Census Bureau. YouthLink covers a near-universe of individuals born in the United States since 1980 and includes detailed information on demographics, place of birth, mortality, parental characteristics, and residential histories. These linked, national individual-level data enable the examination of trends in youth mortality -- a rare outcome in this population -- across time, geography, and subpopulations defined by demographic and socioeconomic characteristics of individuals, their families, and communities. The data also support analyses of the factors contributing to observed mortality patterns. This paper describes the construction of YouthLink, the data sources used in its development, coverage assessment, and plans for future updates to the database.