Cimexomys is an extinct North American mammal that lived from the Upper Cretaceous to the Paleocene.

Age: Lower Paleocene of the Denver Formation in Colorado (United States) "C. arapahoensis is known from four dental and mandiblar fossils from the Alexander Locality of the Denver Formation (Colorado) and is the largest known species of Cimexomyx.

Age: Puercan (Paleocene) of the Polecat Bench Formation in Wyoming (USA).

A near complete dentition and skeletal elements were discovered at Egg Mountain, a site associated with a dinosaur nesting colony, though this wasn't the original material.

C. judithae is reportedly more derived than other species, and the integrity of the genus is suspect, (as reflected here by the later entries for "Cimexomys").

The body mass is estimated to have been around 20 g. Based on the new material from Montana, the authors "argued that Cimexomys is too primitive to be included among either the Taeniolabidoidea or Ptilodontoidea.

This agrees with our conclusion as we tentatively place Cimexomys in the informal "Paracimexomys group", which we erect for plesiomorphic (basal), poorly known members of the Cimolodonta", (Kielan-Jaworowska & Hurum, 2001, p. 393).