The Assize courts were periodic criminal courts. They were active from about 1350 until 1972. These courts were conducted by pairs of judges from the courts at Westminster. The judges worked through circuits which covered most of England.
At first, the assizes reviewed certain property disputes, but gradually their jurisdiction expanded to include criminal cases, as well. Over time, these courts became the principal criminal courts in England and Wales, until they were replaced by Crown Courts by the Courts Act 1971.
Most of England was covered by six circuits: Home, Midland, Norfolk, Northern, Oxford, and Western. Beginning in 1340, each circuit had jurisdiction over a group of counties, as follows:
- Home: Essex, Hertfordshire, Kent, Middlesex, Surrey, and Sussex
- Midland: Derbyshire, Rutland, Leicestershire, Lincolnshire, Northamptonshire, Nottinghamshire, and Warwickshire
- Norfolk: Bedfordshire, Buckinghamshire, Cambridgeshire, Norfolk, Suffolk, and Huntingdonshire
- Northern: Cumberland, Northumberland, Westmorland, and Yorkshire
- Oxford: Gloucestershire, Herefordshire, Shropshire, Staffordshire, and Worcestershire
- Western: Berkshire, Cornwall, Devon, Dorset, Hampshire, Oxfordshire, Somerset, and Wiltshire
You can read more about these courts at https://www.familysearch.org/node/1232