The anti-communist killings of 1965–66 comprised the single most traumatic political event in independent Indonesia, with a consensus estimate of approximately 500,000 deaths. However, these estimates, along with a geographic and political characterization of the killings, have been informed exclusively by anecdotal accounts. In this article, available census data are used in conjunction with demographic analysis to provide a comprehensive and systematic picture of the killings. Using East Java, one of the four hardest-hit Indonesian provinces, as an example, this article estimates and illustrates their impact and provides a geographic characterization of the killings with evidence about the relationship between their locations and local political milieux. While this study is not able to apportion degrees of agency or responsibility for the killings across the various perpetrators, including the Indonesian army and political opponents of the Communist Party of Indonesia, the patterns presented in this article parallel and build on prior research by anthropologists and historians.