The biodemography of isolated populations with a subsistence economy is of special interest because the conditions to which the populations have been subjected are similar to those present over a large part of the history of our species, and hence the conclusions drawn can be extrapolated to other similar populations. In the present work, we used two recently employed techniques (self-organizing maps and Monmonier's algorithm) to study the genetic structure of a small rural region: Fuentes Carrionas (province of Palencia, Spain). The study was based on information contained in marriage registers and family reconstructions for the period 1880–1979. We calculated the coefficients of relationships (Hedrick) among the parishes (by isonymy and parent-offspring matrix) and studied their relationship with geographic distances (Mantel). Then, using Monmonier's algorithm, we examined the genetic barriers. Finally, by applying self-organizing maps, we studied the distribution of surnames. The correlation between genetic distance matrices estimated through surnames and gene flow was high (p < 0.01), and geographic distance was found to be significantly related to both surnames and gene flow (p < 0.01); geographic distance therefore seems to be the main factor of isolation. However, the genetic barriers revealed a region divided in two, and the surname distribution displayed an identical division: 29.56% of the surnames appeared almost exclusively in the northeastern half and 21.91% appeared only in the southwest. Both techniques afforded coherent and complementary results. Their combined use allows a detailed study to be made. Although geographic distance was the strongest determining factor, we detected others factors (orographic and socioeconomic) that seem to have left their mark on the genetic structure of Fuentes Carrionas.