Maricopa County (/ˌmærɪˈkoʊpə/ MARR-i-KOH-pə) is located in the south-central part of the U.S. state of Arizona. The U.S. Census Bureau estimated its population was 4,410,824 as of 2018, making it the state's most populous county, and the fourth-most populous in the United States, containing more than half the population of Arizona. It is more populous than 23 states. The county seat is Phoenix,^[4] the state capital and fifth-most populous city in the United States.

Maricopa County is the central county of the Phoenix-Mesa-Glendale, AZ Metropolitan Statistical Area.

Maricopa County was named after the Maricopa Indians.^[5] There are five Indian reservations located in the county.^[6] The largest are the Salt River Pima-Maricopa Indian Community (east of Scottsdale) and the Gila River Indian Community (south of Chandler).

According to the U.S. Census Bureau, the county has a total area of 9,224 square miles (23,890 km2), of which 9,200 square miles (24,000 km2) is land and 24 square miles (62 km2) (0.3%) is water.^[7] Maricopa County is one of the largest counties in the United States by area, with a land area greater than that of four states. From west to east, it stretches 132 miles (212 km) and 103 miles (166 km) from north to south.^[8] It is by far Arizona's most populous county, encompassing well over half of the state's residents. It is the largest county in the United States to have a capital city.

As of the census of 2000, there were 3,072,149 people, 1,132,886 households, and 763,565 families residing in the county. The population density was 334 people per square mile (129/km²). There were 1,250,231 housing units at an average density of 136/sq mi (52/km²). The racial makeup of the county was 77.4% White, 3.7% African American, 1.9% Native American, 2.2% Asian, 0.1% Pacific Islander, 11.9% from other races, and 2.9% from two or more races. 29.5% of the population were Hispanic or Latino of any race. 19.1% reported speaking Spanish at home.^[17]

There were 1,132,886 households out of which 33.0% had children under the age of 18 living with them, 51.6% were married couples living together, 10.7% had a female householder with no husband present, and 32.6% were non-families. 24.5% of all households were made up of individuals and 7.9% had someone living alone who was 65 years of age or older. The average household size was 2.67 and the average family size was 3.21.

The population was spread out with 27.0% under the age of 18, 10.2% from 18 to 24, 31.4% from 25 to 44, 19.80% from 45 to 64, and 11.7% who were 65 years of age or older. The median age was 33 years. For every 100 females, there were 100.10 males. For every 100 females age 18 and over, there were 98.10 males.

The median income for a household in the county was $45,358, and the median income for a family was $51,827. Males had a median income of $36,858 versus $28,703 for females. The per capita income for the county was $22,251. About 8.0% of families and 11.7% of the population were below the poverty line, including 15.4% of those under age 18 and 7.4% of those age 65 or over.

As of the 2010 census, there were 3,817,117 people, 1,411,583 households, and 932,814 families residing in the county.^[18] The population density was 414.9 inhabitants per square mile (160.2/km2). There were 1,639,279 housing units at an average density of 178.2 per square mile (68.8/km2).^[19] The racial makeup of the county was 73.0% white (58.7% non-Hispanic white), 5.0% black or African American, 3.5% Asian, 2.1% American Indian, 0.2% Pacific islander, 12.8% from other races, and 3.5% from two or more races. Those of Hispanic or Latino origin made up 29.6% of the population.^[18] The largest ancestry groups were:^[20]

Of the 1,411,583 households, 35.1% had children under the age of 18 living with them, 47.8% were married couples living together, 12.4% had a female householder with no husband present, 33.9% were non-families, and 25.9% of all households were made up of individuals. The average household size was 2.67 and the average family size was 3.25. The median age was 34.6 years.^[18]

The median income for a household in the county was $55,054 and the median income for a family was $65,438. Males had a median income of $45,799 versus $37,601 for females. The per capita income for the county was $27,816. About 10.0% of families and 13.9% of the population were below the poverty line, including 19.8% of those under age 18 and 7.0% of those age 65 or over.^[21]

According to data provided by the United States Census Bureau in October 2015 and collected from 2009-2013, 73.72% of the population aged five years and over spoke only English at home, while 20.32% spoke Spanish, 0.56% spoke Chinese, 0.47% Vietnamese, 0.41% Tagalog, 0.37% Arabic, 0.36% German, 0.30% French, 0.25% Navajo, 0.21% Korean, 0.20% Hindi, 0.15% Italian, 0.14% Persian, 0.13% Russian, 0.13% Serbocroatian, 0.12% Telugu, 0.12% Polish, 0.11% Syriac, 0.11% Japanese, 0.11% spoke Romanian, and 0.10% spoke other Native North American languages at home.^[22]

The governing body of Maricopa County is its Board of Supervisors. The Maricopa County Board of Supervisors consists of five members chosen by popular vote within their own districts. Currently, the Board consists of four Republicans, each representing districts in the more affluent or conservative districts of the county, and one Democrat, representing the largest district. Each member serves a four-year term, with no term limits.

The Maricopa County Sheriff's Office provides court protection, administers the county jail, and patrols the unincorporated areas of the county plus incorporated towns by contract.

Maricopa County has a long history of being a Republican Party stronghold. While the city of Phoenix leans towards the Democratic Party, along with some other small areas within the county, the rest of the county tends to vote heavily Republican. Every Republican presidential candidate has carried Maricopa County since 1948. This includes the 1964 presidential run of native son Barry Goldwater, who would not have even carried his own state had it not been for a 21,000-vote margin in Maricopa County. It is currently the largest county in the country to vote Republican. Since 1964, Democrats have only kept the margin to single digits three times–in 1992, 1996, and 2016. In 2018, Democrat Krysten Sinema continued the democratic trend of Maricopa county by carrying it on the way to her statewide victory- the first for democrats since 1988 in both Arizona & Maricopa County.^[23]

Despite its apparent political leanings, Maricopa County voted against Proposition 107 in the 2006 election. This referendum, designed to ban gay marriage and restrict domestic partner benefits, was rejected by a 51.6–48.4% margin within the county, and statewide by a similar margin. Two years later, however, a majority of county residents voted to pass the ultimately successful state constitutional amendment banning same-sex marriage.

Unlike cities and towns in Arizona, counties are politically and legally subordinate to the state, and do not have charters of their own. The Board of Supervisors acts in the capacity of executive authority for the county within the statutes and powers prescribed by Arizona state law. The state legislature devotes considerable time to local matters, with limited discretion granted to the Board of Supervisors on minor ordinance and revenue collection issues. Chair of the Board is held by one member for a period of one year, and is selected by the Board members themselves through public hearing.

The election of the County Sheriff, County Attorney, County Assessor, County Treasurer, Superintendent of Schools, County Recorder, Constables, Justices of the Peace, Clerk of the Superior Court, and retention of Superior Court Judges are also determined by popular vote.

The county's dominant political figure for over two decades (from 1993 to 2017) was Sheriff Joe Arpaio, who had dubbed himself "America's Toughest Sheriff" and gained national notoriety for his flamboyant and often controversial practices and policies.^[25]

As Maricopa County is home to almost 60 percent of the state's population, it dominates Arizona's politics. Eight of the state's nine congressional districts include at least some portion of the county, and five of said districts have their population center located there. Most of the state's most prominent elected officials live in the county, as well.

†Member was originally appointed to the office.

The major primary commercial airport of the county is Sky Harbor International Airport (PHX).

Other airports located in the county include:

In terms of freight rail, the Union Pacific Railroad and the Burlington Northern Santa Fe Railroad serve the county.

In terms of passenger rail, greater Phoenix is served by a light rail system. The county has no other passenger rail transport as Amtrak's Sunset Limited, which served Phoenix until June 2, 1996, has its closest stop in Maricopa in neighboring Pinal County. The train connects Maricopa to Tucson, Los Angeles, and New Orleans three times a week. However it does not stop in Phoenix itself.

The population ranking of the following table is based on the 2010 census of Maricopa County.^[29][30]

† county seat