The Great Western Railway 1000 Class or County Class was a class of 4-6-0 steam locomotive. Thirty examples were built between 1945 and 1947, but all were withdrawn and scrapped in the early 1960s. A replica locomotive is under construction.

These locomotives were the final and most powerful development of the two-cylinder Saint Class introduced in 1901 and included several features that had already been used on the successful Modified Hall class. Hawksworth had hoped to design a new 4-6-2 express locomotive for post war traffic, when he took up office in 1941 but had been prevented by the war from doing so. This scheme was not entirely dead in 1945 when he was given the authority to build another batch of mixed-traffic 4-6-0s. 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 280psi. The boiler was a development that used the tooling for the LMS Stanier Class 8F boiler, Hawksworth being able to study this design closely when 8Fs were being built at Swindon as part of the war effort.

Withdrawals of the class took place between September 1962 and November 1964. No. 1011 County of Chester was the last of the class withdrawn. It was placed in storage before being sold to Cashmore's scrapyard in Newport where it was cut up in March 1965. All were scrapped.

No locomotives of this class survived into preservation. However, a replica is being built at the Didcot Railway Centre, home of the Great Western Society. When completed it will take the name and number of No. 1014 County of Glamorgan. The replica is based around the frames from Modified Hall Class 7927 Willington Hall and the boiler from LMS Stanier 8F 48518. The boiler from the Hall will be used in the replica Grange project at the Llangollen Railway. It will also have a number of smaller original parts off scrapped County locomotives including the chimney from 1006 County of Cornwall.