Talos III was the ringed third planet of the Talosian system within the Talos star group.

In 2254, the position and orbital path of Talos III in an inner system map was displayed on the bridge of the USS Enterprise. The planet was located 2.5 astronomical units from the binary stars of Talos A and Talos B. (TOS: "The Cage", "The Menagerie, Part I", production art)

In the mid-2280s, a cargo container was sent by the Federation from Talos III to Regula. This container was stored in a cave located deep under the surface of this planetoid. (Star Trek II: The Wrath of Khan)

This planet was only mentioned in writing.
According to Star Trek: Star Charts (pp. 37 & 40), Talos III was classified as an L-class planet. This planet was located in the Alpha Quadrant.