Casmus III was a planet in Federation space, in the Alpha or Beta Quadrant, the third planet of the Casmus star system. By the late 23rd century, Casmus III was orbited by Starbase 42. The USS Enterprise-A traveled to the planet in 2287 on its first mission following the starship's visit to Sha Ka Ree. (TOS comics: "The Return!", "The Sentence")

planets visited by the USS Enterprise (NCC-1701-A)
Earth • wishing planet • Gamma Trianguli VI • Christophi IX • Sector 9 Romulan colony • Miraud • Triaminus IV • Endicor • Omicron Ceti IV • Chapin I • Nimbus III • Casmus III • Chronian III • New Brinden • Tau Gamma II • Claneia I • Karimea • Datugad • Needra • Dinar IV • Lerik IV • Rura Penthe • Khitomer • Prestor V • Chal