L-374 I was the uninhabited first planet of the L-374 system. This system was near and in the same sector as the L-370 system, and was near 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.