A "county" is a political administrative sub-unit. In the United States, all states (except Louisiana) are divided into counties, and many state powers are delegated to these sub-units. The number of counties in a state in the US can vary greatly, from more than 250 in Texas to a handful in some smaller states.

In the United States, it's a region or district of land or territory. The word county looks very similar to country, but they are not interchangeable. The U.S. is divided into 50 states, and each state is divided into many counties. Counties contain towns and cities. So we divide our country from state->county->city. Each county also has local government officials. If the state you live in is big and you want to describe where you live to someone, you can tell them the city or county you live in.