Coniasaurus Owen is a small Late Cretaceous marine lizard. Here, we describe two isolated vertebrae of C. cf. C crassidens Owen from the Fairport Chalk Member of the Carlile Shale (Upper Cretaceous) in west-central Russell County, Kansas. This report constitutes the first detailed description of Coniasaurus from the stratigraphic unit. Whereas Coniasaurus has been reported from the Late Cenomanian and Middle Santonian deposits in Kansas, the two vertebrae described here substantiate the presence of the taxon during the early Middle Turonian (ca. 92.1–91.2 Ma), adding a new insight into the paleoecology of the Late Cretaceous Western Interior Sea of North America.