Rather than build more examples of existing designs, Hawksworth introduced the County Class as a testbed for a number of the ideas he hoped to incorporate into the Pacific at a later date.

In addition to the innovations already adopted for the Modified Hall class, the new class contained several further changes from usual Great Western practice including the use of double chimneys on certain members and a high boiler pressure of 280 psi (1.93 MPa) (although this was later lowered in an attempt to reduce maintenance costs).

In the event the standard inside Stephenson link motion of the Churchward and Collett two cylinder classes was used.

The first batch of twenty were built at Swindon Works and delivered between August 1945 and March 1946 (Lot No.

The second batch were given names English and Welsh Counties previously used on the GWR 3800 Class of 4-4-0 tender locomotives that were part of George Jackson Churchward's locomotive standardisation programme in the early days of the 20th century.

The Counties had a mixed reception: some traditionalists regarded them as ‘non-standard, expensive and unnecessary,’[5] others considered them a successful, free steaming design, well suited to express or freight work and a fitting finale to GW two-cylinder 4-6-0 development.

However a replica is being built at the Didcot Railway Centre, home of the Great Western Society.

1014 County of Glamorgan in recognition of the late Dai Woodham's Barry Scrapyard in Glamorganshire from which many withdrawn steam locomotives were saved for preservation.