Multiple paternity is widespread among reptiles in general and turtles specifically. However, its frequency is highly variable even among closely related species. Paternity is an important component of the genetic mating system of a species, and it can provide insight into the social mating system of the species. I investigated the occurrence and frequency of multiple paternity in a population of Blanding's Turtle (Emys blandingii), a rare freshwater species. A high frequency of multiple paternity was detected in this population, with 13 of 16 (81%) clutches showing evidence of siring by multiple males at one locus and nine of 16 (56%) at two or more loci. Multiply sired clutches received approximately equal contributions by both, and rarely three, sires. Therefore, polyandry appears to be the most common reproductive strategy for females in this population. Evidence was also found to suggest that sperm storage between years may occur in this species. The high frequency of multiple paternity observed here suggests that multiple mating may be beneficial to females and/or their offspring. Further research is needed to determine whether this is the case and, if so, how females may benefit from multiple matings.