L-374 I was the uninhabited first planet of the L-374 system. This planet was located within a sector of the Beta Quadrant and was near the L-370 system. This planet was close to the Rigel system.
This was one of two planets spared in the planet killer attack of 2267; the other was L-374 II. The other two planets in the system, L-374 III and L-374 IV, were destroyed. When the crew of the badly damaged USS Constellation was unaccounted for after the planet killer's attack, Spock considered it improbable that the ship's crew had fled to L-374 I, as this planet had a surface temperature of molten lead (approximately 327 °C). (TOS: "The Doomsday Machine")
This planet was only mentioned in dialogue.
The quadrant of origin for this planet was inferred from the trajectory of the planet killer. This ancient machine destroyed, in this order, L-370 and L-374 and the next system targeted was the Rigel system. This system had been established to be in the Beta Quadrant by star charts seen in Star Trek: Enterprise, Star Trek: Discovery, Star Trek: Picard, Star Trek: Strange New Worlds, and Star Trek: Section 31.