Indonesia – home to the world’s largest Muslim population – is an ethnically diverse archipelago with sizeable non-Muslim communities. There is a dearth of demographic study on how religions shape patterns of marriage partnerships in Indonesia. We use full enumeration data from the 2010 Indonesian Population Census to examine the incidence, regional variation, pairing patterns, and socio-demographic correlates of interreligious marriage (irm). We derived a subset of over 47 million co-resident heads of household and their spouses from the 2010 Census. About 228,778 couples (0.5%) were enumerated as having different faiths at the time of the Census. Rates of irm are higher in ethnically diverse provinces. Such findings are likely to underestimate the prevalence of interreligious marriage due to existing regulations and norms that effectively discourage irm, and the associated practice of pre-marital conversions. Our multivariate analysis focused on three provinces with the highest rates of irm: Jakarta, North Sumatra, and West Kalimantan. In Jakarta and North Sumatra, the likelihood of irm is higher among non-Muslims and among those at the higher end of the education spectrum. In these provinces, the likelihood of irm is lower among younger birth cohorts, supporting speculation about stronger institutional barriers against irm over time. This is the first study attempting to derive national and regional estimates of patterns of irm in Indonesia. Given the increasing polemics related to irm and the Indonesian Marriage Law, setting out this research is an important initial step for further study of this issue.