La Paz County is the 15th county in the U.S. state of Arizona, located in the western part of the state. As of the 2020 census, its population was 16,557, making it the second-least populous county in Arizona. The county seat is Parker. The name of the county is the Spanish word for "the peace", and is taken from the early settlement of La Paz along the C…La Paz County is the 15th county in the U.S. state of Arizona, located in the western part of the state. As of the 2020 census, its population was 16,557, making it the second-least populous county in Arizona. The county seat is Parker. The name of the county is the Spanish word for "the peace", and is taken from the early settlement of La Paz along the Colorado River.