The subject of this article is the chancellery and archival analysis of the alderman’s and the magistrate’s book for the town of Kórnik from 1580–1607. At present the manuscript is kept at the headquarters of the State Archives in Poznań. Based on appropriately selected literature and information contained in the book, it was possible to carry out an external and internal critique of the source. It needs to be highlighted that the manuscript has only rarely been as a historiographical archival source.