Las Cruces is the second-most populous city in the U.S. state of New Mexico and the seat of Doña Ana County. As of the 2020 census, its …Las Cruces is the second-most populous city in the U.S. state of New Mexico and the seat of Doña Ana County. As of the 2020 census, its population was 111,385, making Las Cruces the most populous city in both Doña Ana County and southern New Mexico. The Las Cruces metropolitan area had an estimated population of 213,849 in 2017. It is the principal city of the Las Cruces metropolitan statistical area, which encompasses all of Doña Ana County. The city is also part of the El Paso–Las Cruces combined statistical area, a larger trading and marketing region. The combined statistical area has a population of 1,088,420, making it the 56th-largest in the United States.