The primary paper by McColloch and Pitts is "A Logical Calculus of Ideas Immanent in Nervous Activity" (1943) it doesn't use exactly the term "neural net" but i

The primary paper by McColloch and Pitts is "A Logical Calculus of Ideas Immanent in Nervous Activity" (1943) it doesn't use exactly the term "neural net" but it mentions nets, networks, and "nervous nets". But it seems like the term "nervous net" goes back to the 19th century as a description of primitive neural arrangements in biology.