Indonesia is undergoing a third demographic transition that features changes in ethnic composition. We examine quantitatively the extent and change of dominance of the Javanese, who have experienced below replacement fertility. As used herein, an ethnic group is said to be dominant if it is the largest ethnic group and its percentage is at least twice the percentage of the second largest ethnic group. The Javanese are the largest, most ubiquitous and politically important ethnic group in Indonesia. This quantitative analysis addresses the ethnic dominance and cultural hegemony literature. We question the ubiquity of the Javanese – who represent the process of Javanization – because Indonesia’s Javanese character/culture may be eroding. We find that among the Javanese living outside their three home provinces, the percentage of those who speak Javanese daily at home is very low. These Javanese may have adapted to local conditions. We also find that the Javanese are not always the dominant or even the largest ethnic group. In most of the districts, they comprise a very small minority ethnic group. An important finding is that the “third demographic transition” has been and continues to be occurring in Indonesia, a large developing country. Our findings expand the original concept of what constitutes a third demographic transition, which has been applied previously only to developed countries. We conclude that the Javanese are still dominant, but their dominance has declined, and that a third demographic transition is taking place in Indonesia.