Religious affiliation is nowadays getting plenty of attention in Austria, in the public sphere with increased presence in the news and in the policy discourse. The aim of this study is to estimate the religious composition of the population of Vorarlberg in 2018, taking advantage of available data, such as census information and statistics on components of population change. The latest census that collected data on religion was implemented in 2001 and since then population counts have been relying on register data and did not collect data on the religious affiliation of the Austrian population. Therefore, to study changes in the religious composition of the population residing in Vorarlberg, it needs to be estimated using population projections following a methodology that was developed by Goujon et al. (2017) in a project to reconstruct (and project into the future) the population of Austria and Vienna in 2016. The reconstruction shows that Vorarlberg follows similar trends as those observed in Austria since 2001: 1) The share of Roman Catholics declines strongly, 2) there is a strong increase in the population with no religious affiliation, and 3) the share of Muslims has increased substantially which is the outcome of two main trends-fertility and migration. The study of the origin (country of birth) of Muslims residing in Vorarlberg in 2018 points at an increasing Austrian-born population, originating from parents or grandparents born predominantly in Turkey but also at a diversification as a result of the 2015 refugee crisis