Local Governments: USA.gov — USA.gov hosts this page of useful links to sites related to local governments.
Find a County — the National Association of Counties "collects information on counties, such as county officials, courthouse addresses, county seats, cities within a county as well as various statistical and geographical information. To see a listing of the counties for a state, select a State from the map. You are then able to get more detailed information on counties."
U.S. Conference of Mayors: Meet the Mayors — Find a mayor for a given city in the US.