Roads have numerous negative ecological effects on terrestrial fauna, and vehicular mortality can have significant demographic consequences for some species. We studied road mortality of reptiles around Carlyle Lake, Clinton County, Illinois, USA, from April 2000 through November 2002, to assess the impact of vehicular traffic and identify influential factors. Carlyle Lake, a popular tourism/recreation area, is situated in a larger agricultural landscape and is home to the largest Illinois population of the endangered Eastern Massasauga (Sistrurus catenatus). We documented 321 cases of reptile road mortality (84 individuals of six turtle species and 237 individuals of nine snake species) while driving our approx. 46 km study route roundtrip daily. Turtle road mortality was highest in May and June, and positively associated with precipitation and minimum daily temperature. Colubrid snake road mortality was highest in April and October, and positively associated with minimum daily temperature. We recorded 42 cases of road mortality of S. catenatus with the highest number occurring from mid-August to mid-September. Road mortality in S. catenatus was biased toward adult males, which show an increase in movement in August, coinciding with the peak of the mating season and a period of high tourist visitation. The traffic intensity on a road segment did not significantly affect the level of road mortality, but segments through high quality habitats had higher levels of mortality than segments through lower quality habitats. Based on our study on the ecology of S. catenatus, we make recommendations to reduce road mortality that should aid in the conservation of the Carlyle Lake population.