Final answer:
The U.S. Constitution doesn't specify county officers, and the positions vary by state. Common county offices include the sheriff, the county clerk, and the assessor, which are essential in running county government functions such as law enforcement, record-keeping, and tax assessment.
Step-by-step explanation:
According to the Constitution, the three county officers that counties must have are not explicitly outlined in the U.S. Constitution as it delegates powers to the states to establish their own local government systems. However, through various state constitutions and laws, there are common county officials that are often required. Counties typically operate under structures that may include the commission system, the council-administrator system, or the council-elected executive system, and they regularly have offices such as the sheriff, the county clerk, and the assessor. The sheriff is generally in charge of law enforcement, the county clerk manages records and elections, and the assessor handles property tax evaluations. While the detail provided does not specifically list the three constitutional county officers, these roles are crucial in county government functions, which include maintaining public infrastructure, law enforcement, voter registration, and fiscal responsibilities.