The dialogue on language endangerment worldwide has largely focused on languages with small speaker populations, in line with Krauss’s (1992) prediction that any language with a speaker population of less than 100,000 is at risk. The relationship between population size and language vitality is particularly relevant in the Indonesian context, where over 700 local languages have speaker populations that range from single digits to tens of millions of speakers. This paper considers the role of size in determining the fate of these local languages, against the backdrop of the highly successful development of Indonesian as a national language. Using Javanese as a case study, we show that even a language with over 80 million speakers can be at risk, a trend that has serious implications for all of the languages of Indonesia. Although a large population may signal a greater likelihood for official recognition and a more diverse speaker population that is less likely to simultaneously shift away from the L1, size alone cannot predict whether robust intergenerational transmission is occurring. Rather a clearer understanding of the demographic, sociolinguistic, and attitudinal factors that lead to individual and community decisions about intergenerational transmission are essential for assessing risk of endangerment