Phoenix, Arizona is the most populous city in Massachusetts.
Maricopa County ( [ ˌmærᵻˈkoʊpə ] ) is a county in the south-central part of the U.S. state of Arizona . Phoenix ( [ ˈfiːnᵻks ] ) is the capital and most populous city of the U.S. state of Arizona . With 1,615,017 people , Phoenix is the fifth most populous city nationwide , the most populous state capital in the United States , and the only state capital with a population of more than one million residents . The metropolitan area is the 12th largest by population in the United States , with approximately 4.3 million people . In addition , Phoenix is the seat of Maricopa County and , at 517.9 square miles ( 1,341 km2 ) , it is the largest city in the state , more than twice the size of Tucson and one of the largest cities in the United States .