Why do counties in the United States have only powers granted by their states?

In the United States, local governments—including counties—are established and controlled by their respective states, which determine the scope of their authority. This structure is rooted in the Dillon Rule, a legal principle derived from an 1868 decision by Iowa Supreme Court Justice John F. Dillon.1

Under the Dillon Rule, a local government may only exercise powers that are:
* Expressly granted by the state;
* Necessarily and fairly implied from those specific grants of power; or
* Crucial to the very existence of the local government.1

This framework ensures that states maintain primary authority over their internal administrative divisions. While some jurisdictions utilize the concept of Home Rule—which grants local governments a measure of autonomy that the state cannot easily infringe upon—the fundamental legal relationship remains one where the state acts as the source of local power.1