The answer to this question depends upon where you live. Each individual city is governed by a mayor and city council. A county is a political subdivision of the State, and provides State and local services to its residents. Since its leaders are elected by local residents, a county can tailor State programs to meet the unique needs of its citizens. Both cities and counties deliver municipal services, such as police, fire protection, libraries, animal control and street maintenance.
Counties also deliver services to both city and county residents.
The County also manages specially-designated County Services Areas in localities where residents have chosen to organize and assess annual fees to provide specific services. Special Districts, typically governed by Boards of Directors, also provide specialized services within their jurisdictions. The Riverside County Privacy Policy is available for viewing here.