T'lli Beta
T'lli Beta was an inhabited planet in the T'lli Beta system. This was the homeworld of the T'lli Betans. This planet was located somewhere in the Alpha or Beta Quadrant.
In 2367, the USS Enterprise-D was en route to T'lli Beta before it was ensnared by the gravitational pull of a cosmic string fragment which a group of two-dimensional beings were attempting to enter. (TNG: "The Loss")
In 2371, the location of T'lli Beta was labeled in the star chart Data and Picard were studying in stellar cartography aboard the USS Enterprise-D. (Star Trek Generations, okudagram)
In the Star Trek Encyclopedia, 3rd ed., p. 489, it was stated that this planet was named after script writer Hilary J. Bader's grandmother, Tillie Bader.