The species of Colletes Latreille from Brazil, Paraguay and/or Uruguay are revised through an integrative approach to taxonomy combining morphological and molecular data to delineate species. Herein, the following 19 species are recognized and illustrated, eight of them described as new: C. altimontanus Ferrari & Silveira, C. argentinus Friese, C. chicoi n. sp., C. cyaneus Holmberg, C. ferenudus n. sp., C. flagellaris n. sp., C. furfuraceus Holmberg, C. hawkingi n. sp., C. imbricatus n. sp., C. kerri Moure, C. meridionalis Schrottky, C. michenerianus Moure, C. ornatus Schrottky, C. pampeanus n. sp., C. petropolitanus Dalla Torre, C. rufipes Smith, C. rugicollis Friese, C. sertanicola n. sp., and C. sexangulus n. sp. To facilitate their recognition, diagnoses, detailed descriptions and redescriptions, and a fully-illustrated key for all species are provided.