Rio Arriba County is a county in the U.S. state of New Mexico. As of the 2020 census, the population was 40,363. Its county seat is Tierra Amarilla. Its northern border is the Colorado state line.

Española is a city primarily in Rio Arriba County, New Mexico, United States. A portion of the central and eastern section of the city is in Santa Fe County. Founded as a railroad village some distance from the old Indian town of San Juan de los Caballeros, it was named Española and officially incorporated in 1925. It has been called the first capital city in the United States. At the time of the 2010 census, the city had a total population of 10,495. Española is within the Albuquerque–Santa Fe–Las Vegas combined statistical area.