Rural communities in Okayama Prefecture, like those throughout Japan and the remainder of the industrialized world, have undergone rapid economic and social changes in the post-war period. Both policy makers and scholars who are interested in social change in rural areas need to develop an understanding of what those changes have been, what they might be leading to and what the impacts of those changes have been on communities and the people who live there, if they are to effectively promote the social health of these communities. This paper is the first in a series of articles which will carry out such an investigation using the hamlet communities of Okayama Prefecture as the primary data base. This first paper, through an analysis of data on these communities collected by the Japanese Ministry of Agriculture, Fisheries and Forestry will present findings which will delineate the main structural changes which these hamlets underwent in the 1960 to 1980 period. Basically, it will be shown that the two most important factors explaining the evolution of the current structure of these communities are their size and their proximity to major urban areas. While the effects of rapid industrialization have led to a decrease in the importance of agriculture throughout all of the hamlets of the prefecture, the new form into which a hamlet has evolved depends in large measure on its physical location within the prefecture, and its size, as measured by the number of houses and area of cultivated land.