Discovery of a single specimen of brachyuran decapod from the Campanian Millwood Member in southern Manitoba, Canada, permits description of a new genus and species, Cretacocarcinus smithi. Comparison of sternal architecture and general carapace morphology with potentially related taxa documents that the new genus, along with Camarocarcinus Holland and Cvancara, form a new family, Camarocarcinidae, tentatively assigned to the Raninoidea. The Camarocarcinidae are interpreted to have originated in the upper Midcontinental Seaway in the Late Cretaceous, survived the K-T extinction event(s), and dispersed into southern North Dakota, USA; Greenland; and Denmark in the Paleocene.