New Mexico, constituent state of the United States of America. It became the 47th state of the union in 1912. New Mexico ranks fifth among the 50 U.S. states in terms of total area and is bounded by Colorado to the north, Oklahoma and Texas to the east, Texas and the Mexican states of Chihuahua and Sonora to the south, and Arizona (which was part of the Territory of New Mexico from 1850 to 1863) to the west. At its northwestern corner New Mexico joins Arizona, Utah, and Colorado in the only four-way meeting of states in the United States. The capital of New Mexico is Santa Fe