I know "county" is an administrative unit in the United States, but what makes it different from "city" or town"?

Native speaker’s answer
Rebecca
A county is the biggest political and administrative jurisdiction (i.e. the biggest local government district) within a state in America. Most states and territories have at least two types of local government: counties (which are the biggest) and municipalities (otherwise known as cities, which are smaller). Sometimes, counties are further divided into townships (which are similar to towns). Thus, you can consider the order to be: state > county > municipality. Ex: The county has lifted its mask mandate. Ex: The county police have jurisdiction over all the townships in the area.