List of counties in New Mexico in the context of Arizona Territory

Rio Arriba County (Spanish: Condado de Río Arriba) 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.

Rio Arriba County comprises the Española, New Mexico, micropolitan statistical area, which is also included in the Albuquerque–Santa Fe–Los Alamos combined statistical area.

Los Alamos County (English: "The Poplars" or "Cottonwoods"; Spanish: Condado de Los Álamos) is a county in the U.S. state of New Mexico. As of the 2020 census, the population was 19,419. The smallest county by area in the state, Los Alamos County was formed from parts of Sandoval and Santa Fe counties on June 10, 1949. The county has two census-designated places: Los Alamos and White Rock.

The land that eventually became Los Alamos County was administered exclusively by the U.S. federal government during and for a few years after the Manhattan Project.

Bernalillo County (/ˌbɜːrnəˈliːjoʊ/) is the most populous county in the U.S. state of New Mexico. As of the 2020 census, the population was 676,444. The county seat, Albuquerque, is the most populous city in New Mexico. Bernalillo County is the central county of the Albuquerque, NM Metropolitan Statistical Area.

Taos County is a county in the U.S. state of New Mexico. As of the 2020 census, the population was 34,489. Its county seat is Taos. The county was formed in 1852 as one of the original nine counties in New Mexico Territory.

Taos County comprises the Taos, New Mexico Micropolitan Statistical Area.

Eddy County is a county located in the U.S. state of New Mexico. As of the 2020 census, the population was 62,314. Its county seat and largest city is Carlsbad. The county was created in 1891 and later organized in 1892. It is north of the Texas state line.

Eddy County comprises the Carlsbad-Artesia, NM Micropolitan Statistical Area.