La Union is in Dona Ana County, and in the Southwest New Mexico region. This community is located south of Las Cruces and just north of El Paso, Texas on the Rio Grande, just off Interestate 10. La Union is part of the Las Cruces, New Mexico metro area.
Two early Mexican settlements in the 1800's combined to form "La Union". These settlements were "Los Ojitos" and "Los Amoles". Everyone suffered from periodic flooding of the Rio Grande River washing out home and crops. Therefore, they moved to higher ground. Today locals are aware of both "new" and "old" La Union. The "new" community is "La Union Nueva", along NM Highway 28, and the "old" is "La Union Vieja", west along NM Highway 182.