New records of a rare dragonfly, Stylurus plagiatus, are described from the Hudson River estuary in eastern New York State. Breeding occurred primarily in tidal mudflats; however, in other parts of its range, this species is known to use a broader array of habitat types. As a southerly species at its northern range margin, populations of S. plagiatus in eastern New York are likely to be temperature-limited, although other factors, such as shoreline habitat integrity and dispersal behavior, may also play a role in defining its range limits.