Tarminster was a town in England.
In the 1970s, Farrel's Plastics, the plastics factory, at which the Master's plotted to awaken the Nestene Consciousness and use Autons to take over Earth, was in Tarminster. (TV: Terror of the Autons)
Again, in the 1970s, the Third Doctor and Jo are returning from a scientific conference at Tarminster University. (PROSE: The Clean Air Act)
In 2009, Sarah Jane Smith tracked Travast Polong to a hospital in Tarminster. (TV: The Mark of the Berserker)
Behind the scenes
According to the official Saxon website, Lucy Saxon's father was Lord Cole of Tarminster.