The New Mexico Territory became an organized territory of the United States on September 9, 1850, and it existed until New Mexico became the 47th state on January 6, 1912.

The western portion of New Mexico came from the Treaty of Guadalupe Hidalgo in 1848, while the remainder of eastern New Mexico (from the Rio Grande to the present New Mexico-Texas border) was added as consequence of the Compromise of 1850. The Gadsden Purchase of 1853 added a smaller additional area to New Mexico Territory—the southernmost strip of Arizona and New Mexico.

The land contained in the original 1850 New Mexico Territory was the western portion of the future state, plus most of future Arizona (known as Santa Ana County), a small part of Colorado, and Nevada south of 36° 30' N. The Texan cession and the Gadsden Purchase expanded the territory greatly, but the establishment of Colorado Territory on February 28, 1861 and of Arizona Territory on February 24, 1863 (west of the 109th meridian) left New Mexico with its present boundaries.

As the route to California, New Mexico and Arizona were disputed territory during the American Civil War, resulting in an attempt to join the Confederate States of America and the Battle of Glorieta Pass.

See also

• Governors of New Mexico Territory
• Historic regions of the United States