Styxosaurus is named for the mythological River Styx (Στυξ), which separated the Greek underworld from the world of the living. The -saurus part comes from the Greek sauros (σαυρος), meaning "lizard" or "reptile." The type specimen was found on Hell Creek in Logan County, Kansas and is the source of the genus name coined by Samuel Paul Welles, who described the genus, in 1943.