The Mouvement de la Population et de l’État civil is a very rich data source which offers new possibilities for the study of demographic diversity in rural Belgium. In fact, this data source provides yearly information on several demographic variables at the municipal level from the 19th century on. However, the use of raw data has important limitations due to the small numbers: the small population of the municipalities, especially the rural ones, produces inaccurate indicators affected by random fluctuations. The purpose of this article is twofold. On the one hand, it presents the strengths of the data source, and in particular the advantages it offers to the study of Belgian rural areas. On the other hand, it suggests a solution to the small numbers problem, which consists of a simplified territorial division and the use of a moving average in order to smooth the time series. The discussion is based on the example of a simple indicator of the timing of marriage.