A county is a type of officially recognized geographical division within a modern country, federal state, or province. Counties are defined in diverse ways, but they are typically current or former official administrative divisions within systems of local government, and in this sense counties are similar to shires, and typically larger than municipalities. Various non-English terms can be translated as "county" or "shire" in other languages, and in English new terms with less historical connection have been invented such as "council area" and "local government district". On the other hand, in older English-speaking countries the word can still refer to traditional historical regions such as some of those which exist in England, Scotland, Wales, and Ireland. The term is also sometimes used for districts with specific non-governmental purposes such as courts, or land registration.

Historically the concept of a geographical administrative "county" is European (from French: comté, Latin: comitatus), and represented the territorial limits of the jurisdiction of a medieval count, or a viscount (French: vîcomte, Latin: vicecomes) supposedly standing in the place of a count. However, there were no such counts in medieval England, and when the French-speaking Normans took control of England after 1066 they transplanted the French and medieval Latin terms to describe the pre-existing Anglo Saxon shires, but they did not establish any system placing the administration of shires under the control of high-level nobles. Instead, although there were exceptions, the officers responsible for administrative functions, such as tax collection, or the mustering of soldiers, were sheriffs, theoretically assigned by the central government, and controlled directly by the monarch.

The Counties of England have evolved in several different directions, so that there is now more than one definition. The 39 "traditional", "ancient" or "historic" counties of England have on the one hand evolved into 83 metropolitan and non-metropolitan counties, which are modern administrative districts covering the whole country except London, Berkshire, and the Isles of Scilly. The historic counties are also the basis for the 48 ceremonial counties of England, which still each have lords-lieutenants and high sheriffs, who theoretically represent the monarchy in different parts of the country. In cases such as Yorkshire and Sussex, some historical counties remain as geographical regions without any administrative function. The postal counties of the United Kingdom, based upon older county definitions, were used by the Royal Mail until 1996. Scotland replaced its 34 historic counties or shires with 32 modern "council areas", some of which correspond to the old counties, or use the old names. In Wales the modern "principal areas" correspond to some extent to the old county boundaries, and they can also still be referred to as "counties" and "county boroughs". The 32 modern Irish counties were first defined after the Norman invasion, but several of these were broadly continuations with earlier divisions clan lordships (Tír Eoghain became county Tyrone, Tír Chonaill became county Donegal, west Breifne became county Leitrim and Fír Manach became modern county Fermanagh).

Notable examples of more recently-founded English-speaking administrations which have taken up the term "county" as a level of local government include the United States and Canada, where counties sometimes evolved from historic districts governed by courts or magistrates, before the countries became independent of the United Kingdom. In New Zealand there were counties historically, but these have been replaced by cities or districts. In Australian local government, the term "shire" is among the several which are typically used in local government, depending upon the state, but the term "county", which was used by the colonial administration, is mainly relevant for land registration districts (for example in Queensland lands administration). It is also used for the County Court of Victoria, which is a court covering an entire Australian state.

Counties are the current second-level political division in Kenya. Each county has an assembly where members of the county assembly (MCAs) sit. This assembly is headed by a governor. Each county is also represented in the Senate of Kenya by a senator. Additionally, a women's representative is elected from each county to the Parliament of Kenya to represent women's interests. Counties replaced provinces as the second-level division after the promulgation of the 2010 Constitution of Kenya.

Liberia has 15 counties, each of which elects two senators to the Senate of Liberia.

The English word county is used to translate the Chinese term xiàn (县 or 縣). In Mainland China, governed by the People's Republic of China (PRC), counties and county-level divisions are the third level of regional/local government, coming under the provincial level and the prefectural level, and above the township level and village level.

There are 1,464 so-named "counties" out of 2,862 county-level divisions in the PRC, and the number of counties has remained more or less constant since the Han dynasty (206 BC – AD 220). It remains one of the oldest titles of local-level government in China and significantly predates the establishment of provinces in the Yuan dynasty (1279–1368). The county government was particularly important in imperial China because this was the lowest level at which the imperial government is functionally involved, while below it the local people are managed predominantly by the gentries. The head of a county government during imperial China was the magistrate, who was often a newly ascended jinshi.