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")
This planet was only mentioned in dialogue.
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.