In 1887, John Bartholomew's Gazetteer of the British Isles described Barnard Castle like this:
Barnard Castle, market town and township, Gainford par., Durham, on river Tees, 15 miles W. of Darlington by rail -- township, 40l7 ac., pop. 4269; town (extending into Startforth par., Yorkshire), 632 ac., pop. 4544; 3 Banks, 1 newspaper. Market-day, Wednesday. The Town Hall dates from 1747, and St Mary's Church (restored 1871) from the end of the 12th century. ...
The ruined castle, from which the town takes its origin, was founded (1180) by Barnard Baliol, grandfather of John Baliol; it is the scene of part of Sir Walter Scott's "Rokeby." The chief mfrs. are carpets, woollen cloth, and hats. Barnard Castle has become popular as a health resort; there is a chalybeate spring 2 miles distant. The Duke of Cleveland, who owns the manor, takes hence the title of viscount and baron.
GB Historical GIS / University of Portsmouth, History of Barnard Castle, in Teesdale and County Durham | Map and description, A Vision of Britain through Time.
Date accessed: 25th March 2017
Click here for more detailed advice on finding places within A Vision of Britain through Time , and maybe some references to other places called " Barnard Castle ".