Genetic variation among human populations can reflect a combination of contemporary patterns of gene flow and genetic drift as well as long-term population relationships due to population history. We examine the likely impact of past history and contemporary structure on the patterns of anthropometric variation among 31 counties in Ireland (made up of the two nations of the Republic of Ireland and Northern Ireland). Data for 17 anthropometric measures and parent-offspring migration on 7,214 adult Irish males were taken from the large data set originally collected by Dupertuis and Dawson in the mid-1930s (Hooton et al., 1955). Patterns of genetic similarity among 31 counties were assessed using R matrix methods that allow estimation of minimum genetic distances. These distances were compared to distances reflecting history, geography, and migration using matrix permutation methods. The results indicate that among-group variation in Ireland reflects past population history to a much greater extent than contemporary patterns of migration and population size. The midland counties are distinct from other populations, and their history suggests greater genetic input from early Viking invasions. A second major pattern in biological variation is a longitudinal gradient separating western and eastern counties. This gradient appears related to patterns of early settlement and/or a concentration in the east of later immigrants, particularly from England. Comparison of regional means with published data for several other European nations confirms these hypotheses.