Mesa is a city in Maricopa County, Arizona, United States. It is the third-most populous city in Arizona, after Phoenix and Tucson, the 36th-most populous city in the U.S., and the most populous city that is not a county seat. The city is home to 504,258 people as of 2020. It is the most populous city in the East Valley of the Phoenix metropolitan area. It is bordered by Tempe on the west, the Salt River Pima–Maricopa Indian Community on the north, Chandler and Gilbert on the south along with Queen Creek, and Apache Junction on the east.