Mesilla is a town in Doña Ana County in the U.S. state of New Mexico.
It was formed in 1848, after the Treaty of Guadalupe Hidalgo shifted the U.S.-Mexico border south of the village of Doña Ana, placing it in the United States. A small group of Mexican citizens, unhappy at being part of the United States, chose to move south of the border, and by 1850, Mesilla was an established colony.
America declared the Mesilla Valley region part of the United States following the establishment of Fort Fillmore in 1851 to protect its citizens north of the border from repeated Apache attacks. The resulting boundary dispute was eventually resolved in 1853, with the Gadsen Purchase, when Mesilla became a part of the United States.
Famous for its markets, cantinas and festivals, it was the most important town of the region up until the 1880s. It quickly declined in importance after the Santa Fe Railway opted to build their railroad through neighbouring Las Cruces in 1881.