Studies that document changes in long-lived species are valuable in determining how demographic and environmental changes are affecting populations. This study documents apparent declines in Eastern Hellbender (Cryptobranchus alleganiensis) populations over the last 20 years in the Allegheny River drainage of New York State. We compared current mark–recapture data to similar data collected in the 1980s at eight sites using a comparable method of capture (rock turning). In addition, we employed several other methods of capture including trapping, bank searching, and night lighting. Despite these extra efforts, the number of Hellbenders captured was less than the number captured historically. Hellbenders were extirpated from a single site and the ecological density (number of individuals per 10 m² of habitable area) decreased in several other sites relative to the 1980s. Current and historical populations contained more mature adults than juveniles, but we found more Hellbenders <20 cm total length at five sites compared to the 1980s study. The sex ratio changed from predominantly female in the 1980s to predominantly male currently. Eggs in nests were found in both studies, although little is known about egg or larval survival and overall recruitment. Although demographic issues such as reproduction and recruitment may be contributing to Hellbender declines in the Allegheny drainage, these do not appear to have changed drastically from the 1980s. Other possible causes of decline include factors such as land use changes, introduced species, or some other environmental issue.