5 Most Populated Counties in the US

4. Maricopa County, Arizona

Population Estimates (2023): 4,585,871

With a population of 4.5 million, Maricopa County is the fourth largest county by population in the US, and the 5th largest in Arizona by area. About 8.2% of individuals under 65 in Maricopa County live with disabilities, and 10.5% of the population lacks health care coverage. At the same time, there are about 104,022 employer establishments in the county and it has a median household income of $83,747.