Tachyoryctes rex is found on the western slope of Mount Kenya, Kenya, at in altitude. It is common in a limited area, at the upper edge of the bamboo forest and lower edge of the moorland. A female found on October 5 had a large embryo. T. rex builds large mounds with diameters up to . Some have interpreted these mounds as being built by termites instead. From those mounds, burrows may extend up to and be up to deep. One chamber is used for urination and defecation and to store plant matter; it produces a substantial amount of heat. In other chambers, T. rex builds large nests of grass. The animal eats plant roots. Its presence results in a change in vegetation on the mounds, which have fewer grasses and more woody plants, either because the animal eats plant roots or because the soil is altered.