The paper focuses on the contribution of regional 18th-century ‘East Prussian’ historiography to the formation of an Old Prussian identity. The author specifies the concept of ‘Old Prussianism’, and reveals the main steps in the change in that model of identity in the 18th century through an analysis of three authors who were active in Königsberg and spanned three generations: Michael Lilienthal (1686–1750), Daniel Heinrich Arnoldt (1706–1775) and Georg Christoph Pisanski (1725–1790). On the basis of their treatises, the paper reveals how in the 18th century, in the territory of the former Duchy of Prussia, a unique regional self-awareness independent of Royal (Polish) Prussia and of Brandenburgian Prussia was developing, as well as a related concept of the past of the region.