There are 74 US Post Offices in Maricopa County serving a total of 2,238,470 residents equating to 30,250 residents per post office. It's estimated that approximately 3,572,848 packages are handled across the 74 county post offices annually. Maricopa County (/\u02ccm\u00e6r\u1d7b\u02c8ko\u028ap\u0259/ MARR-i-KOH-p\u0259) is a county located in the south-central part of the U.S. state of Arizona. As of the 2010 census, its population was 3,817,117, making it the most populous county in the state, and the fourth-most populous in the United States. It is more populous than 23 states. The county seat is Phoenix, the state capital and sixth-most populous city in the country. Maricopa County is the central county of the Phoenix-Mesa-Glendale, AZ Metropolitan Statistical Area. The population explosion is evident in a 2007 Forbes study which ranked four of Maricopa County's municipalities in the top ten fastest-growing cities in the nation. Those included Buckeye as the second-fastest-growing city, Surprise and Goodyear as 3rd and 4th, and Avondale as 9th. All four of these cities are located in the growing \"West Valley\", which is the area of Maricopa County to the west of the city of Phoenix. Maricopa County was named after the Maricopa Indians. There are five Indian reservations located in the county. The largest of these are the Salt River Pima-Maricopa Indian Community (east of Scottsdale) and the Gila River Indian Community (south of Phoenix)."