A county town is the 'capital' of a county in the United Kingdom or Republic of Ireland. County towns are usually the location of administrative or judicial functions, or established over time as the de facto main town of a county. The concept of a county town eventually became detached from its original meaning of where the county administration is based (see County halls below). In fact, many county towns are no longer part of "their" administrative county e.g. Derby is administered by a unitary authority entirely separately from the rest of Derbyshire. Many county towns are in fact cities, but all are referred to as county towns irrespective of whether city status is held or not.

Note that in Eastern Canada and the United States of America, the term county seat is usually used for the same purpose. However, in the state of Louisiana the term parish seat is used instead.

1. Lent assizes were held at Reading, where the county gaol and house of correction were situated; summer assizes were held at Abingdon, which was the site of the county bridewell. Knights for the shire were nominated at Reading and elected at Abingdon.Samuel Lewis, A Topographical Dictionary of England, Vol. I, 1831
2. Sir John Baldwin, Chief Justice of the Common Pleas, caused the county assizes to be moved to Aylesbury. Knights for the shire continued to be elected at Buckingham. The 1911 Encyclopædia Britannica considered Buckingham to be the county town.
3. The County Assize Court sat at Bodmin, and the 1911 Britannica considered Bodmin to be the county town. Launceston was also historically considered the county town.
4. Knights of the Shire were elected at Cockermouth
5. East Kent and West Kent had separate administrations until 1814, with East Kent sessions meeting at Canterbury, and West Kent at Maidstone, the over-all county town.
6. Knights of the Shire were elected at Brentford; sessions presided over by Middlesex Justices of the Peace were held at Clerkenwell; trials for persons accused of the most serious crimes took place in the Old Bailey before the Aldermen of the City prior to the committing of the accused to Newgate Prison (which functioned as the county gaol for Middlesex) if found guilty; while the county council had its headquarters at the Middlesex Guildhall in Westminster from its establishment in 1889 until its abolition in 1965.Justice in Eighteenth-Century Hackney (Process and Procedures), by Ruth Paley British History Online
7. Alnwick's position as the county town seems to have been based largely on its castle being the seat of the Duke of Northumberland, although Knights of the Shire were elected at the town too. Assizes for the county however were held mainly or exclusively in Newcastle-upon-Tyne. Morpeth Castle was used as the prison for Northumberland, and the county gaol was built there in 1824.
8. Knights of the Shire were elected at Ilchester. Somerton temporarily became the county town in the late thirteenth century, when the shire courts and county gaol were moved from Ilchester.
9. Southwark is listed as the county town by Stewart (1828). Quarter Sessions were held at Newington by Southwark.
10. Horsham was occasionally described as the county town of Sussex due to the presence of the county gaol and the periodic holding of the county assizes and quarter sessions in the town. The last assizes were held there in 1830, while the gaol was closed in 1845.General history of Horsham - The town as county centre, Victoria County History of Sussex, Volume VI British History Online
11. Wiltshire County Council note that Wiltshire "never had a well recognised county town". Wilton had served as the seat of Quarter Sessions and for election of Knights of the Shire until 1832. Knights had been nominated at Devizes. A 1870s gazetteer describes "Salisbury and Devizes" as the "county towns". The 1911 Encyclopædia Britannica names only Salisbury.