Mesilla is also a spider genus (Anyphaenidae).Mesilla (also known as La Mesilla and Old Mesilla) is a town in Doña Ana County, New Mexico, United States. The population was 2,180 at the 2000 census. 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.Mesilla Plaza is a National Historic Landmark.