Most of what is now Maricopa County was included as part of the Territory of New Mexico until 1863, when the Arizona Territory was established. The growth of Phoenix and other settlements along the Salt River resulted in the creation of Maricopa County - officially established on February 14, 1871. It was the first new county of the original four counties of Territorial Arizona. The County was named in honor of the Maricopa Indians, who were known to have inhabited the area as early as 1775. Maricopa County’s outer geographical boundaries were set in 1881 and have not changed since.