Eighteen rodent species are recognized from the Fitterer Ranch fauna of North Dakota based on more than a thousand collected specimens. Of the species recognized, four are new: the prosciurine aplodontids Prosciurus hogansoni and Altasciurus leonardi, the heliscomyid Heliscomys borealis and the cricetid Eumys lammersi. A previously described castorid from this fauna, Oligotheriomys primus Korth, 1998, is considered a synonym of “Eutypomys” magnus Wood, 1937, on the basis of the recovery of lower dentitions, but is retained in the genus Oligotheriomys. A single specimen is questionably referred to Microparamys, a genus elsewhere limited to the earlier Eocene (Clarkforkian-Chadronian Land Mammal Ages). The rodent fauna appears to be a combination of predominantly Orellan and Whitneyan species (early Oligocene), suggesting that the section might transcend the Orellan-Whitneyan boundary. However, the rodent fauna does not alter significantly from the lowest to the highest horizons.