Monument is accepted to be the first Anglo settlement in Lea County by James Cook, who built a store, appropriately enough named Cook’s Store. He used to pick up the mail in Carlsbad and bring it back to the settlement until around 1900 when the postal service granted permission to establish its own post office. It took its name from an old water source named Monument Springs.

The water source known as Monument Springs was located about ten miles west of the Texas border. Believed to have been previously used by native tribes for water, it was discovered by a detachment of the United States Army out of Fort Davis, Texas under Colonel William R. Shafter. Col. Shafter is noted for having directed the building of a seven and one half foot tall structure of native limestone rock to mark the area. This monument no longer exists and the stone is thought to have been reused in early dwellings.