The Great Western Railway 3800 Class, also known as the County Class, were a class of 4-4-0 steam locomotives for express passenger train work introduced in 1904 in a batch of ten. Two more batches followed in 1906 and 1912 with minor differences. They were designed by George Jackson Churchward, who used standard components to produce a four-coupled version of his Saint Class 4-6-0s.

They were the last new GWR 4-4-0 design and by far the most modern, with inside frames and outside cylinders. They were designed as a part of Churchward's standardisation plan but were found to have a front end too powerful for the wheel arrangement and all were withdrawn by the early 1930s.  

No members of the class were preserved. However, the Great Western Society took the decision to create the next locomotive in the sequence, 3840 County of Montgomery. The project has been handed over to the Churchward County Trust and 3840 will be based at the Gloucestershire Warwickshire Railway following its construction at Tyseley Locomotive Works in Birmingham.

The locomotive is being built with both new parts, such as the driving wheels which have been cast using the pattern created for GWS Saint Class 2999 "Lady of Legend", and recycled standard parts recovered from former Barry scrapyard locomotives including the Standard No. 4 Boiler, the pony truck wheel set, 2 x pony truck axle boxes, 4 x horn guides and 2 x eccentric sheaves from 5205 Class 2-8-0T 5227, and 4 x driving wheel axle boxes from 2800 Class 2-8-0 2861.