Both small-scale human societies and personal social networks have a characteristic hierarchical structure with successively inclusive layers of 15, 50, 150, 500, and 1,500 individuals. It has been suggested that these values represent a set of natural social attractors, or “sweet spots,” in organizational terms. We exploited the new phenomenon of permanent (i.e., residential) campsites to ask whether these values are present in the size distribution of the numbers of residents in these naturally small-scale communities. In two separate data sets of different grain, we find consistent evidence for sites with 50, 150, 500, and maybe 1,500 residents. We infer that these reflect numerical sizes at which communities may in some way be socially optimal. Our data do not allow us to say why this pattern emerges, but the consistency of the results and the fact that the predetermined sizes of permanent campsites adhere to this pattern suggest that it may arise from the limits on the number of relationships that make an effective community.