The Darla system was a Delta Quadrant planetary system.

In 2377, the system was part of the Antarian Trans-stellar Rally's course. In this system, the number eight ship cut off the number three ship. In an effort at making up for lost ground, the number three ship changed course by using the gravity of a gas giant in this system to boost its speed. (VOY: "Drive")

This system was only mentioned in dialogue.
According to Star Trek: Star Charts (p. 94), the gas giant was the fourth planet in the system.