Monticello is an unincorporated community located in Sierra County, New Mexico, United States. Monticello is located on Alamosa Creek 22 miles northwest of Truth or Consequences. Monticello has a post office with ZIP code 87939.Monticello was laid out in 1856, and named after Monticello, New York, the former home of an early settler. A post office called Monticello has been in operation since 1881.