A map of the Sigma Draconis system
Sigma Draconis VII was the seventh planet in the Sigma Draconis system. This was one of six planets in this system that was not classified as M class. (TOS: "Spock's Brain")
While in command and recording his only log entry in TOS, Sulu inadvertently called Sigma Draconis VI "Sigma Draconis VII". Kirk also inadvertently refers to Sigma Draconis VI as "Sigma Draconis VII" in his own later captain's log, even though he himself referred to the planet as "VI" twice earlier in the episode.
According to the Star Trek: Star Charts (pgs. 19, 44), Sigma Draconis VII was located in Sector 004 (Sigma Draconis sector).