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County police are police forces existing primarily in the United States that possess primary jurisdiction over an entire county. England and Wales, two constituent countries of the United Kingdom (UK), are policed by territorial police forces which are largely formed on a county basis. Historically, Sweden and Scotland, another constituent country of the UK, have had county police, although both countries now have unified national police services.
Until the end of 2014, all of the 21 counties of Sweden had its own County Police Department. In 2015, Sweden merged all local police departments into a single police agency, dividing the country into seven police regions instead.
Police forces in Scotland and Wales also used to be organised on a county basis, but then were amalgamated into a number of larger regional forces: eight in Scotland and four in Wales. In 2013, Scotland ditched its eight regional forces and created one national police force known as Police Scotland.
Northern Ireland is historically policed on a national basis, first by the Royal Irish Constabulary, then the Royal Ulster Constabulary, which was reformed in 2001 as the Police Service of Northern Ireland. Northern Ireland has never been policed on a county basis.
Other Special Police Services that have a presence at a country level are in operation throughout the UK, such as the British Transport Police who mainly police the transport services such as public trains, train stations, buses, bus stations & trams in the UK. The Nuclear Constabulary which is responsible for providing law enforcement and security at or within 5 km of any relevant nuclear site and for nuclear materials in transit within the United Kingdom. The Ministry of Defence Police of which their primary responsibilities are to provide armed security and to counter terrorism, as well as uniformed policing and investigative services to Ministry of Defence property, personnel, and installations throughout the United Kingdom. Others also include the Royal Military Police, Royal Navy Police, Royal Air Force Police and more.
In the United States, the powers, duties, and even existence of county police forces vary widely depending on the state, and even on the particular county within a state. County police forces as autonomous entities are relatively rare and tend to exist only in metropolitan counties. Many states also have a sheriff's office which are always formed on a county basis and traditionally carry out duties related to the functioning of the courts and legal system, such as service of process, executing legal writs, and protection for the local courthouse and its judges. Many state constitutions mandate that the position of sheriff be created, which leads many states to also give sheriffs the duties of a county police to avoid having overlapping departments with similar duties, leaving the sheriff as the exclusive law enforcement agency for a county. Some counties that previously had both a county police force and a sheriff's office have merged the two, leaving the sheriff in command of the unified force, as the sheriff derives his power directly from the constitution; the most prominent example of such a merger is the Las Vegas Metropolitan Police Department which is actually led by the county sheriff despite its name.
County police tend to fall into three broad categories:
- Full-service police departments, which provide the full spectrum of police services to the entire county, irrespective of local communities, and may provide contractual security police services to special districts within the county.
- Hawaii has only county police; there are no local police.
- Limited service police departments, which provide services to unincorporated areas of the county (and may provide services to some incorporated areas by contract), and usually provide contractual security police services to special districts within the county.
- Restricted service police departments, which provide security police duties to county owned and operated facilities and parks. Some may also perform some road patrol duties on county built and maintained roads, and provide support to municipal police departments in the county.
Note: County detectives, who are maintained in the northeastern states by county attorneys' offices, fall within this category. In the state of Louisiana, a county is known as a parish. In the state of Alaska, a county is known as a borough. The only of which to have their own police department is North Slope Borough.
There are 3,141 counties in the United States and some county police departments are:
A to M
- Albemarle County Police Department, Albemarle County, Virginia - full service
- Allegany County Bureau of Police, Allegany County, Maryland - full service, a division of the Allegany County Sheriff's Office.
- Allegheny County Police Department, Allegheny County, Pennsylvania - County-wide Authority - Detective Div.- Uniform patrol county facilities and property.
- Anne Arundel County Police Department, Anne Arundel County, Maryland - full service
- Arlington County Police Department, Arlington County, Virginia - full service
- Athens-Clarke County Police Department, Clarke County, Georgia - full service
- Baltimore County Police, Baltimore County, Maryland - full service
- Bergen County Police Department, Bergen County, New Jersey - (Merged with the Bergen County Sheriff's Office and renamed "Bureau of Police Services" on 1/1/2015)
- Broome County Sheriff's Department, Broome County, New York - full service
- Broomfield Police Department, City and County of Broomfield, Colorado - full service
- Broward County Department of Law Enforcement, Broward County, Florida- limited service
- Cobb County Police Department, Cobb County, Georgia- Full service
- Camden County Police Department, Camden County, New Jersey - limited service
- Charlotte-Mecklenburg Police Department, Mecklenburg County, North Carolina - full service
- Chesterfield County Police Department, Chesterfield County, Virginia - full service
- Clark County Park Police, Clark County, Nevada - restricted service
- Clayton County Police Department, Clayton County, Georgia - limited service
- Cook County Sheriff's Office, Cook County, Illinois - limited service
- DeKalb County Sheriff's Office, DeKalb County, Alabama - full service
- Dougherty County Police Department, Dougherty County, Georgia- limited service
- DeKalb County Police Department, DeKalb County, Georgia - limited service (By statute, DKPD has authority throughout the entire county, but yields this authority to incorporated municipalities that provide their own police services.)
- Delaware County Courthouse and Park Police Department, Delaware County, Pennsylvania - restricted service
- Denver Police Department, City and County of Denver, Colorado - full service
- Fairfax County Police Department, Fairfax County, Virginia - full service
- Floyd County Police Department, Floyd County, Georgia - full service
- Floyd County Sheriff's Office, Floyd County, Georgia - limited service
- Fulton County Sheriff's Office, Fulton County, Georgia - limited service
- Gaston County Police Department, Gaston County, North Carolina - limited service
- Glynn County Police Department, Glynn County, Georgia
- Gwinnett County Police Department, Gwinnett County, Georgia - full service (serves unincorporated Gwinnett County, and the cities of Berkeley Lake, Buford, Dacula, Grayson, Rest Haven, Peachtree Corners, and Sugar Hill)
- Hawai‘i County Police Department, Hawaii County, Hawaii - full service
- Henrico County Police Department, Henrico County, Virginia - full service
- Henry County Police Department, Henry County, Georgia - limited service
- Honolulu Police Department, City and County of Honolulu, Hawaii - full service
- Horry County Police Department, Horry County, South Carolina - limited service (full-time service of all unincorporated areas of Horry County, South Carolina and part-time service of certain municipalities within the county by contract)
- Houston County Sheriff's Department, Houston County, Georgia - limited service
- Howard County Police Department, Howard County, Maryland - full service
- Howard County Sheriff's Office, Howard County, Maryland - limited service (full-time service for eight geographical sectors in Howard County) 
- James City County Police Department, James City County, Virginia - full service
- Johnson County Sheriffs Department, Johnson County, Kentucky -Full Service
- Kauai County Police Department, Kauai County, Hawaii - full service
- Kenton County Police Department, Kenton County, Kentucky - limited service
- Las Vegas Metropolitan Police Department, Clark County, Nevada - limited service
- Lexington Division of Police, Fayette County, Kentucky - full service
- Los Alamos County Police Department, Los Alamos County, New Mexico- full service
- Louisville Metro Police Department, Louisville and Jefferson County, Kentucky
- Maryland-National Capital Park Police Department, Montgomery County, Maryland and Prince George's County, Maryland - restricted service
- Maui County Police Department, Maui County, Hawaii - full service
- Metropolitan Nashville Police Department, Davidson County, Tennessee - full service
- Miami-Dade Police Department, Miami-Dade County, Florida - limited service
- Montgomery County Police Department, Montgomery County, Maryland - full service
- Morris County Park Police Department, Morris County, New Jersey - restricted service
- Red County Sheriff's Office, Red County, San Andreas - full service, Sheriff Roy James Bradley
N to Z
- Nassau County Police Department, Nassau County, New York - full service
- New Castle County Police Department, New Castle County, Delaware - full service
- New Orleans Police Department, Orleans Parish, Louisiana - full service
- New York City Police Department, covers five New York counties, Bronx County, Kings County, New York County, Queens County, and Richmond County - full service
- Oldham County Police Department, Oldham County, Kentucky - limited service
- Onondaga County Sheriff's Office, Onondaga County, New York - full service
- Orangeburg County Sheriff’s Office,Orangeburg County, South Carolina- Full service
- Philadelphia Police Department, Philadelphia County, Pennsylvania - full service
- Pima County Park Police Department, Pima County, Arizona - restricted service
- Prince George County Police Department, Prince George County, Virginia - Full Service
- Prince George's County Police Department, Prince George's County, Maryland - Full service
- Prince William County Police Department, Prince William County, Virginia - Full service
- Polk County Police Department, Polk County, Georgia - limited service
- Riley County Police Department, Riley County, Kansas - full service
- Roanoke County Police Department, Roanoke County, Virginia - full service
- St. Joseph County Police Department, St. Joseph County, Indiana - limited service
- St. Louis County Police Department, St. Louis County, Missouri - full-service
- San Francisco Police Department, City and County of San Francisco, California - full service
- St. Charles County Police Department, St. Charles County, Missouri- full service
- Savannah-Chatham Metropolitan Police Department, Chatham County, Georgia - limited service (serves the city of Savannah and unincorporated Chatham County)
- Spotsylvania County Sheriff's Office, Spotsylvania County, Virginia
- Suffolk County Park Police Department, Suffolk County, New York - restricted service
- Suffolk County Police Department, Suffolk County, New York - limited service
- Union County Police Department, Union County, New Jersey - restricted service
- Westchester County Department of Public Safety, Westchester County, New York - restricted service
- Westmoreland County Park Police Department, Westmoreland County, Pennsylvania - restricted service
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- "Virginia County vs. Town vs. City". Virginia Places.Org. Retrieved October 29, 2016.
- "County Police Departments". Archived from the original on October 29, 2016. Retrieved October 29, 2016.
- "Auxiliary Police and Part Time Law Enforcement Officer Training Standards" (PDF). Virginia Department of Criminal Justice Services. DCJS VA. Retrieved October 29, 2016.
- Howard County, Maryland Sheriff's Office
- Howard County Sheriff's Office Patrol Operations