Rockland County is the second-southernmost county on the west side of the Hudson River in the U.S. state of New York, after Richmond County. It is part of the New York metropolitan area. As of the 2020 U.S. census, the county's population is 338,329, making it the state's third-most densely populated county outside New York City after Nassau and neighboring Westchester Counties. The county seat and largest hamlet is New City. Rockland County is accessible via the New York State Thruway, which crosses the Hudson to Westchester at the Tappan Zee Bridge ten exits up from the NYC border, as well as the Palisades Parkway five exits up from the George Washington Bridge. The county's name derives from "rocky land", as the area has been aptly described, largely due to the Hudson River Palisades. The county is part of the Hudson Valley region of the state.

The administrative divisions of New York are the various units of government that provide local services in the American state of New York. The state is divided into boroughs, counties, cities, towns, and villages. They are municipal corporations, chartered (created) by the New York State Legislature, as under the New York State Constitution the only body that can create governmental units is the state. All of them have their own governments, sometimes with no paid employees, that provide local services. Centers of population that are not incorporated and have no government or local services are designated hamlets. Whether a municipality is defined as a borough, city, town, or village is determined not by population or land area, but rather on the form of government selected by the residents and approved by the New York State Legislature. Each type of local government is granted specific home rule powers by the New York State Constitution. There are still occasional changes as a village becomes a city, or a village dissolves, each of which requires legislative action. New York also has various corporate entities that provide local services and have their own administrative structures (governments), such as school and fire districts. These are not found in all counties.