San Mateo, NM has a population of 578 and is the 18,659th largest city in the United States. The population density is 120 per sq mi which is 598% higher than the New Mexico average and 32% higher than the national average. The median age in San Mateo is 53 which is approximately 43% higher than the New Mexico average of 37. In San Mateo, 82% of the population over 15 years of age are married, 81% speak English and 12% speak Spanish. 56% of San Mateo residents were born in New Mexico, 36% were born out of state, 2% were born outside of the United States and 6% were foreign born.