Mesilla (also known as La Mesilla and Old Mesilla) is a town in Doña Ana County, New Mexico, United States. It is part of the Las Cruces Metropolitan Statistical Area. During the American Civil War, Mesilla briefly served as capital of the Confederate Territory of Arizona. The Mesilla Plaza is a National Historic Landmark.
The village of Mesilla was incorporated in 1848, after the Treaty of Guadalupe Hidalgo moved the U.S.–Mexico border south of the village of Doña Ana, placing it in the United States. A small group of citizens, unhappy at being part of the United States, decided to move south of the border. They settled in Mesilla at this time.
The median income for a household in the town was $42,275, and the median income for a family was $51,181. Males had a median income of $30,500 versus $25,000 for females. The per capita income for the town was $25,922. About 6.3% of families and 9.4% of the population were below the poverty line, including 7.4% of those under age 18 and 5.8% of those age 65 or over.