Based upon the classifications by the U.S. Census Bureau, there are thirty-three cities that also function as county governments, in three different forms:

Areas with governments legally designated as city-counties and
operating primarily as cities:

 Alaska
  City and borough of Anchorage
  City and borough of Juneau
  City and borough of Sitka
  City and borough of Yakutat
 California
  City and county of San Francisco
 Colorado
  City and county of Broomfield
  City and county of Denver
 Hawaii
  City and county of Honolulu
 Kansas
  Unified Government of Wyandotte County and City of Kansas City
 Montana
  Anaconda-Deer Lodge County
  Butte-Silver Bow County

Areas designated as metropolitan governments and
operating primarily as cities:

Tennessee
  Hartsville and Trousdale County
  Lynchburg and Moore County
  Nashville and Davidson County

Areas having certain types of county offices, but as part of another government (city, township, special district, state):

 Florida
  County of Duval (City of Jacksonville)
 Georgia
  County of Clarke (City of Athens)
  County of Muscogee (City of Columbus)
  County of Richmond (City of Augusta)
 Hawaii
  County of Kalawao (State of Hawaii)
 Indiana
  County of Marion (City of Indianapolis)
 Kentucky
  Lexington-Fayette Urban County
 Louisiana
  Parish of East Baton Rouge (City of Baton Rouge)
  Parish of Lafayette (City of Lafayette)
  Parish of Orleans (City of New Orleans)
  Terrebonne Parish Consolidated Government
 Massachusetts
  County of Nantucket (Town of Nantucket)
  County of Suffolk (City of Boston)
 New York
  Counties of Bronx, Kings, New York, Queens, and Richmond (all part of the
  City of New York)
 Pennsylvania
  County of Philadelphia (City of Philadelphia)

Source:
2002 Census of Governments, Volume 1, Number 1, Government Organization, GC02(1)-1,  Washington, DC: United States Department of Commerce, Bureau of Census. Appendix B.