The Mussentuchit local fauna, upper Cedar Mountain Formation (Cretaceous: Albian–Cenomanian), Utah, includes the geologically oldest marsupials: Kokopellia juddi, described previously, and three new taxa named herein. Adelodelphys muizoni, new genus and species, and Sinbadelphys schmidti, new genus and species, both unassignable to family, are among the smallest of Cretaceous marsupials; Pariadens mckennai, new species, tentatively assigned to Stagodontidae, is among the largest. The three are morphologically similar: they bear certain dental specializations of Marsupialia (e.g., presence of labial postcingulid and “twinning” of hypoconulid and entoconid on lower molars), but are plesiomorphic with respect to most or all Late Cretaceous marsupials in other features (e.g., relatively lingual position of conules, lack of stylar cusps C or D on upper molars). Compared to Late Cretaceous (Cenomanian– Maastrichtian) assemblages of North America, the marsupials of the Mussentuchit local fauna are rare and low in morphologic and taxonomic diversity. Biogeographic origin of Marsupialia and their antiquity in North America remain unknown. However, patterns of diversification and differentiation suggest that the taxa from the Cedar Mountain Formation lie near the base of North America's Cretaceous marsupial radiation.