That there was a decline in population between 1850 and 1870 is agreed by all authorities. This fact makes it very attractive to accept Cook's proposed density of 10 persons per house for the Hupa in aboriginal times. But there are two objections to this procedure. For one thing, the population figures for 1870 may be inaccurate. In the census of that year, there were reported 874 Indians of all tribes on the Hoopa Reservation (Kroeber, 1925a, p. 131). But in the same year another agent reported only 649 Indians on the reservation. This is a 25 per cent reduction, and if we reduce the population estimate of 640 by 25 per cent, we get 480 as the estimate for 1870 and a density per house of 5.9. If we raise the population of 480 to account for the 1850-1870 reduction, we are again close to the figure 7.5 persons per house. This calculation is presented merely to indicate that the figures are not reliable. The other objection to accepting Cook's proposed figure for density is that the established figure for the Yurok is 7.5 persons per house. According to Cook, this figure was based on an underlying assumption that "the social family in the usual monogamous tribe included the father, mother, children, and occasional close relatives" (Cook, 1956, p. 99). As a matter of fact, Kroeber's estimate is not based on this assumption but is an empirical estimate based on population counts and house counts (Kroeber, 1925_a_, pp. 16-19), and the figure is accepted wholeheartedly by Cook for the Yurok (1956, p. 83). But what is certainly clear is that the social organization, house type, and environment of the Hupa was virtually the same as that of the Yurok and therefore the population density per house must have been the same. It is therefore clear that we must accept either 7.5 persons per house or 10 persons per house as the population density for both the Hupa and the Yurok, and the question becomes one of comparing the reliability of the figures given for the Yurok with those given for the Hupa. Yurok figures appear to be intrinsically more reliable and are also earlier and I have therefore taken 7.5 persons per house as the density. The population for the Hupa then comes to 1,475 as compared to 2,000 estimated by Cook and to less than 1,000 estimated by Kroeber.