The basic divisions in the United States are: state, county and municipality [an incorporated city, town or township with its own government]. There may also be named but unincorporated villages and settlements, especially in large rural counties. And there may be named places which are, administratively speaking, part of a larger municipality. For example [in the state of Massachusetts], Charlestown is a named place that has existed since earliest colonial times. It was originally a separate town but is now a section or neighborhood of Boston, not a municipal entity in its own right; nevertheless, it is always known by its own name to people in Massachusetts.
In all states, counties have been split or amalgamated over the course of time as have incorporated and unincorporated villages, towns and cities. For this reason, an old gazetteer may not correspond to current administrative reality. In the older and smaller eastern states [especially in New England], counties tend to be less important administratively because most land lies within the jurisdiction of some municipality. This is not the case in the newer, larger and more rural midwestern and western states where much of the land exists outside of incorporated municipalities and is administered by a county government.
In the midwest and west, geographical space is also divided into named townships which are [ideally but not always] squares measuring 6 x 6 miles. These were created when the federal government was surveying and opening up land for settlement. These survey townships may or may not have evolved into modern political units depending on local circumstances. Historical works may refer to these townships. For example, my grandfather was born in Douglas Twsp., a rural area in Marquette County, Wisconsin. It was not a town in the ordinary sense of the word but, rather, a geographical area.
You can read about US counties, municipalities and townships and how they vary in definition and nature from state to state at Wikipedia.
http://en.wikipedia.org/wiki/Political_divisions_of_the_United_Stateshttp://en.wikipedia.org/wiki/County_%28United_States%29http://en.wikipedia.org/wiki/Township_%28United_States%29
