This paper considers the charge that—contrary to the current widespread assumption accompanying the near-universal neglect of his work—Wilhelm Jerusalem (1854–1923) cannot count as one of the founders of the sociology of (scientific) knowledge. In order to elucidate the matter, Jerusalem's "sociology of cognition" is here reconstructed in the context of his own work in psychology and philosophy as well as in the context of the work of some predecessors and contemporaries. It is argued that while it shows clear discontinuities with the present-day understanding of the sociology of (scientific) knowledge, Jerusalem's sociology of cognition was not only distinctive in its own day but also anticipated in nuce a much-discussed theme in current history of science.