Remains of mesomammals, i.e. intermediate-sized mammals, are ubiquitous in southern African fossil sites. Even though they do not constitute a taxonomically cohesive group, medium-sized mammals share common ecological traits and are subject to similar taphonomic processes, making them essential for understanding past ecosystems. This study focuses on craniodental remains of medium- and large-sized rodents and lagomorphs from the Early Pleistocene hominin-bearing site of Cooper’s Cave in the Cradle of Humankind. The Cooper’s D deposit, dated to approximately <1.4 Ma, has provided a wealth of faunal material, including many mesomammal remains. This contribution presents an updated taxonomic analysis of fossil material, including morphological descriptions with new diagnostic criteria, ecological information about the different taxa, and preliminary taphonomic observations. Notably, this assemblage documents the oldest known occurrence of the genus Geosciurus in South Africa, pushing its attested presence back by over one million years.