The Romaine Formation of the Mingan Islands, Québec, contains a limited trilobite fauna of five genera (Bolbocephalus, Peltabellia, Petigurus, Strigigenalis, Strotactinus) with Lower Ordovician Ibexian (Floian) affinity, succeeded by two genera (Acidiphorus, Pseudomera) of early Middle Ordovician Whiterockian (Dapingian) affinity. Trilobites of later Whiterockian (Darriwillian) affinity are more abundant in the overlying Mingan Formation, with 29 genera (Amphilichas, Bathyurus, Calyptaulax, Ceraurinella, Cybeloides, Dolichoharpes, Encrinuroides, Eobronteus, Eorobergia, Failleana, Glaphurina, Glaphurus, Hibbertia, Hyboaspis, Illaenus, Isotelus, Kawina, Nieskowskia, Phorocephala, Pandaspinapyga, Pliomerops, Remopleurides, Sphaerexochus [including S. valcourensis n. sp.], Sphaerocoryphe, Stenopareia, Thaleops, Thulincola, Uromystrum, and Vogdesia). Lectotypes are selected for Mingan species of Illaenus, Peltabellia, Petigurus, Sphaerexochus, Stenopareia, and Thaleops. A number of genera form biofacies which can be related to lithofacies. Taken together with Chazy Group and Northwest Territories trilobite faunas, Mingan trilobites provide critical information on late Whiterockian trilobite distributions in Laurentia in far more detail than seen in the stratotype area of Nevada.