Since the 1960s Irish fertility has undergone dramatic change. While the broad outlines of both the nature and the origins of such change are, by now, well enough known and understood, little attention has been paid to the way in which changes in age specific fertility have been manifested regionally. This paper uses cluster analysis to group counties and county boroughs/cities according to their age-specific profiles of fertility at each full census year between 1961 and 2002 and then ANOVA to identify meaningful statistical relationships between cluster membership in each year and variables descriptive of the demographic and socio-economic context. By 1981 younger fertility profiles had spread from south eastern areas to almost all regions, but during the 1980s older fertility profiles became increasingly characteristic throughout western and northern districts. Despite the on-going, nation-wide ageing of fertility profiles since 1991, this basic regional distinction has remained largely intact. Prior to 1981 changing marriage patterns and family planning among older women seem to have underpinned profile change. Thereafter, however, profile change.patterns seem to have socio-economic and perhaps cultural contextual origins.