Kreisstadt

A county town is usually the location of administrative or judicial functions within the county, or it has been 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 or county hall is based. In fact, many county towns are no longer part of the administrative county. For example, Nottingham is administered by a unitary authority entirely separate from the rest of Nottinghamshire. Many county towns are classified as cities, but all are referred to as county towns regardless of whether city status is held or not.

This list shows county towns prior to the reforms of 1889.

Note – Despite the fact that Belfast is the capital of Northern Ireland, it is not the county town of any county. Greater Belfast straddles two counties (Antrim and Down).

With the creation of elected county councils in 1889 the location of administrative headquarters in some cases moved away from the traditional county town. Furthermore, in 1965 and 1974 there were major boundary changes in England and Wales and administrative counties were replaced with new metropolitan and non-metropolitan counties. The boundaries underwent further alterations between 1995 and 1998 to create unitary authorities and some of the ancient counties and county towns were restored. (Note: not all headquarters are or were called County Halls or Shire Halls e.g.: Cumbria County Council's HQ up until 2016 was called The Courts and have since moved to Cumbria House.) Before 1974 many of the county halls were located in towns and cities that had the status of a county borough i.e.: a borough outside of the county council's jurisdiction.

...
Wikipedia