This project investigates the cognitive linguistic categories that structure the Old Irish landscape lexicon. The semantics of basic landscape vocabulary are differentiated based on collocate analysis and close reading of relevant text passages. Terms are compared across subdomains in order to identify linguistic categories that apply to the overall landscape lexicon. The analysis shows distinctions of (a) domesticated vs. wild landscape features, and (b) landmarks vs. non-landmarks. These distinctions are motivated by a combination of the interactional properties (a, b) and the independent salience (b) of the landscape features. Understanding the cognitive linguistic categories of Old Irish landscape vocabulary provides insight into how medieval Irish society conceptualized the natural world.