For much of its history, the island of Ireland was divided into 32 counties (Irish language contae or condae, pronounced kʊndeː). Two historical counties, County Desmond and County Coleraine, no longer exist, while several county names have changed.

After the partition of Ireland in 1921, what eventually became the state of Ireland comprised 26 of these, with Northern Ireland comprising the remaining six. The counties of Northern Ireland are no longer used for local government, and two former counties in the Republic have been subdivided, giving a modern total of 29 counties for administrative purposes rather than 26. The newer counties, such as Dun Laoghaire-Rathdown and Fingal, are often ignored as much as possible (outside administrative matters) as being non-traditional. In addition, the larger cities are administratively equivalent to counties.

The traditional 32 counties had previously been adopted by sporting and cultural organisations such as the Gaelic Athletic Association, which organises its activities on GAA county lines, and today they still attract strong loyalties, particularly in the sporting field.

In Irish usage, the word county nearly always comes before rather than after the county name; thus "County Clare" in Ireland as opposed to "Clare County" in Michigan. The former "King's County" and "Queen's County" were exceptions; these are now County Offaly and County Laois.