I would argue that the first mention of a structure similar to a blockchain was in a research paper by Haber and Stornetta in 1991. The paper was titled “How to Time-Stamp a Digital Document”
In their scheme a client sends a document to timestamp to a timestamping service. The server would sign the document with the current timestamp and also include a link to the previous document. The pointer points to a piece of data (not a location) So if the data changed the pointer would become invalid.
In my opinion this is just like a blockchain except it is used for documents instead of digital money.