The Texas panhandle is a region of the U.S. state of Texas consisting of the northernmost 26 counties in the state. The panhandle is a square-shaped area bordered by New Mexico to the west and Oklahoma to the north and east. It is adjacent to the Oklahoma Panhandle, land which Texas previously claimed. The 1820 Missouri Compromise declared no slavery would be allowed in states admitted from the Louisiana Purchase above 36°30′ north latitude. Texas was annexed in 1845 from still more westerly land. The Compromise of 1850 removed territory north of this line from Texas, and set the border between the Texas Pandhandle and the New Mexico Territory at the 103rd meridian west. The eastern border at the 100th meridian west was inherited from the Adams–Onís Treaty of 1819, which defined the border between the United States and New Spain. The Handbook of Texas defines the southern border of Swisher County as the southern boundary of the Texas Panhandle region.

New Mexico is a landlocked state in the Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also borders Texas to the east and southeast, Oklahoma to the northeast, and the Mexican states of Chihuahua and Sonora to the south. New Mexico's largest city is Albuquerque, and its state capital is Santa Fe, the oldest state capital in the U.S., founded in 1610 as the government seat of Nuevo México in New Spain.