Family archives are a source of information of the first order for the knowledge of the past. However, many times the transfer of a noble title from one lineage to another, or the neglect on the part of its own holders, has caused its disappearance. Such is the case of the Archive of the former Marquesado de Lanzarote, now unaccounted for and scarcely mentioned by historiography. Although, locating an inventory of it, made in 1634, allows us to know what was in the archive at that time and enables us to reconstruct it, as far as possible, together with the use of other documentary sources such as court records, in which there are numerous copies, transferred from their originals, which were presented as evidence in investigations and trials. In this study, what is shown is the value of the files and judicial files for the reconstruction of the missing family files.