The board of commissioners is the oldest form of county government in the US and is still very common. In a county commission form of government, a body of elected commissioners serves both the executive and the legislative duties, meaning they enact local ordinances and administer them. They approve budgets, oversee spending and hire county employees. The commission usually consists of three to five officials. In some states, they are known as supervisors.

The commissioners are responsible to the voters, but their duties are defined and controlled by the state constitution and state statutes. Their actions can be overturned by state courts. Some department heads, such as sheriff, clerk, treasurer and coroner, are elected rather than appointed by the commissioners.

When many counties were still rural, the duties of the board of commissioners were limited. They kept vital records, assessed property, administered elections and maintained roads. With the spread of suburbs, many counties grew in population and began offering a far wider range of services. It is not unusual today for a board of commissioners to oversee consumer protection, economic development, planning, environmental quality and social welfare programs.

Other duties that the board of commissioners may be responsible for or oversee include:

Issuing bonds Managing county parks Collecting and disposing of trash Managing pensions for county employees Assuring water quality Administering courts and jails Collecting property and sales taxes

In recent decades, government reform movements have criticized the commission form of county government for not having a single chief executive in charge. Some counties have moved to one of two related forms of government in an effort to solve the issue:

Commission-administrator: The elected commissioners appoint a separate professional administrator who carries out policies, hires and fires employees, and prepares a budget for the commission's approval. Council-executive: Voters elect one person as county executive along with a council that serves as the county legislative body. In some areas, the executive can veto laws enacted by the council and exercise other executive powers.