Ostracods of the family Entocytheridae are obligate ectosymbionts, primarily of crayfishes. Although the distribution and diversity of crayfishes is well known in the northeastern US, little is known about entocytherids in this region. In this study, we examined 5 species of crayfishes—Procambarus acutus (White River Crayfish), Orconectes limosus (Spinycheek Crayfish), Orconectes propinquus (Northern Clearwater Crayfish), Cambarus bartonii (Common Crayfish), and Cambarus robustus (Big Water Crayfish)—from 3 counties in New York (Saratoga, Orange, and Tompkins) and 8 counties in New Jersey (Essex, Sussex, Atlantic, Burlington, Camden, Cumberland, Gloucester, and Ocean). We recovered 2 species of entocytherid ostracods: Donnaldsoncythere cayugaensis and Donnaldsoncythere donnaldsonensis. Records from our study expand the known range of D. cayuagensis and fill in gaps in the known range of D. donnaldsonensis.