Longitudinal data for studying fertility in the U.S. are limited in size, making it difficult to fully understand fertility below the national level. However, the Census Bureau makes restricted-use administrative birth data available through the Census Numident for nearly all U.S. births for more than the last century, and most births since 1997 are linked to parents through the Census Household Composition Key (CHCK). These data are not well-known and underutilized to study births in the U.S. We describe the creation and contents of these data sets as well as compare the data to published U.S. vital statistics. We also analyze the geographic coverage of both data sets and compare demographic characteristics to national demographic breakdowns. The fertility information is compared to survey data at the individual level. Finally, the data availability and access for researchers are described.