2012 Census of Governments

From Census.gov:

The Census of Governments identifies the scope and nature of the nation's state and local government sector; provides authoritative benchmark figures of public finance and public employment; classifies local government organizations, powers, and activities; and measures federal, state, and local fiscal relationships.

The data are available by:

level of government (state, local, or state and local combined),
type of government (state, county, city, township, special district, school district), and
category of governmental activity