Many volumes have been written about the family pedigree studies produced by the Eugenic Record Office (ERO) in Cold Spring Harbor, N.Y., but little attention has been paid to the everyday process and purpose of eugenics field research. This paper focuses on the production of one of the ERO’s last family studies, Dwellers in the Vale of Siddem (1919), by A.C. Rogers and Maud Merrill, to explore the creation of eugenic knowledge and the growing power of state institutions in the emerging welfare state. The first half of the paper draws on the correspondence and reports of two female field researchers who were paid by the ERO but supervised by Rogers, the superintendent of the Minnesota School for the Feebleminded. It explores how the conflicting viewpoints of county officials, neighbours, and eugenicists were shaped into a single story of feeblemindedness and degeneracy, and considers how some local officials may have used eugenics field research to deal with families they saw as an economic and social burden. Eugenics field research functioned as a kind of institutional extension work, at least in rural Minnesota. It strengthened the relationships between county officials and the state institution and paved the way for a compulsory institutionalization law. The paper then turns to the book itself, comparing the researchers’ field notes to the published text and commenting on the inconsistencies. Dwellers in the Vale of Siddem was published two years after Rogers died, and it is considered insubstantial even by the standards of ERO family studies. Yet if the book itself had little value as research or propaganda, the process of eugenics research was important. It extended the institution’s influence and disciplinary power into remote communities and lay the foundation for the state’s eugenic sterilization law.