[1] Four counties (Mohave, Pima, Yavapai and Yuma) were created in 1864 following the organization of the Arizona Territory in 1862.

All but La Paz County were created by the time Arizona was granted statehood in 1912.

[3] Under Arizona laws, a county shall not be formed or divided by county initiative unless each proposed county would have all of the following characteristics: (1) at least three-fourths of one percent of the total state assessed valuation and at least the statewide per capita assessed valuation; (2) a population of at least three-fourths of one percent of the total state population according to the most recent United States decennial census; (3) at least one hundred square miles of privately owned land; (4) common boundaries with either (a) at least three other existing or proposed counties; or (b) at least two other existing or proposed counties and the state boundary.

[6] Under the Arizona Constitution, counties are politically and legally creatures of the state, and do not have charters of their own.

The state legislature devotes considerable time to local matters, with limited discretion granted to the Board of Supervisors on minor ordinance, zoning, and revenue collection issues.