This paper draws on a novel dataset crowdsourced from publicly available online genealogies to study demographic change and development in Europe before modern censuses became available. Using millions of publicly available family trees, I reconstruct fertility from horizontal lineages and identify migration to and from urban centers. Then, I systematically compare the data to a range of representative sources in thirty countries and show that selection is limited after the mid-seventeenth century. Finally, I document novel stylized facts on the rural flight, the demographic transition, and the intergenerational persistence of migration, fertility, and longevity; providing suggestive evidence that substantial changes took hold in the eighteenth century, in the early stages of the transition from stagnation to growth.