Talos I was the first planet in the Talosian system, which was located within the Talos star group.

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

This planet was only mentioned in writing.
According to Star Trek: Star Charts (pp. 37 & 41), Talos I was classified as a B-class planet. This planet was located in the Alpha Quadrant.