Farmington is a city in San Juan County in the U.S. state of New Mexico. As of the 2020 census, the city had a population of 46,624 people. F…Farmington is a city in San Juan County in the U.S. state of New Mexico. As of the 2020 census, the city had a population of 46,624 people. Farmington makes up one of the four metropolitan statistical areas in New Mexico.