Trillius Prime was the inhabited prime planet in its star system. (ENT: "Broken Bow")
Trillius Prime was one of the regular destinations of the Earth Cargo Service ships in the 22nd century. Travis Mayweather visited this planet in the sixth grade. It took three years for the ECS Horizon to get there. (ENT: "Broken Bow")
Background information[]
This planet was only mentioned in dialogue.
Travis Mayweather was born in 2126 (ENT: "Broken Bow", "Fortunate Son") and was fifteen in 2141 (ENT: "Bound"). Assuming that the education system of the 22nd Century is largely the same as the 21st Century, and a sixth grader is normally eleven years old, he would have visited this planet in 2137.
In "Two Days and Two Nights", the Enterprise, a NX-class starship, became the first Earth ship to travel 90 light years from its homeworld. Trillius Prime was visited by Humans prior to this event, and thus presumably was closer.
According to "Horizon", the top speed of the ECS Horizon was warp 2, which corresponded to 8 times the speed of light according to the warp chart seen in "First Flight". This suggests that Trillius Prime was located about 24 light years away from Earth.
According to Star Trek: Star Charts (p. 33), Trillius Prime was another name for the planet Trill. However, the Star Trek Encyclopedia, 4th ed., vol. 2, p. 420, 421 does not consider Trillius Prime as being an alternative name for Trill. The authors believed there were two planets, the Trill homeworld and Trillius Prime. This work located Trillius Prime in the Trillius system.
According to StarTrek.com, Trillius Prime was located in the Alpha Quadrant. [1](X)