The island of Seili, in the south-western archipelago of Finland, is famous for its history as a leprosy colony and mental asylum. The island formed a small, hierarchical community run by priests and hospital officials. In this article, we examine the history of the burial crypt in Seili church by comparing information from historical documents and observations made during archaeological fieldwork. The material gathered from these two sources is conflicting, suggesting an interesting history in the use of the burial crypt. It seems that women’s coffins could easily be moved elsewhere from the crypt when new coffins belonging to males were interred. It is argued that identifying the buried individuals would be necessary for a taphonomic study of the mummification processes and ensuring that the information about the crypt is based on facts. However, the identification is difficult due to inconsistent historical records. This underlines the importance of Post-Medieval archaeology in studying sites connected to family histories.