© Wiltshire Museum, Devizes
This is Mawarden Court in 1805 in one of 690 drawings of Wiltshire Churches, houses, and other ancient buildings, in ten volumes, the “Collections for Wiltshire," by John Buckler, F.S.A., (b. 1770, d. 1851) prepared for the library at Stourhead and acquired by the Wiltshire Museum in 1916.
It shows the east front with the E layout of two symmetrical gable wings with a smaller central one that became all the rage in Elizabethan times.
The north wing where the Reading Room now stands was demolished around 1835 and between then and the Tithe map of 1839 the remaining exposed southern wall became the new outer northern wall of a new northern gable, which was closer to the southern to give today’s twin gables. The porch was rebuilt between them. The outbuildings seen in the
painting north of the main house were also demolished around the same time, they stood where the Reading Room car park now is.
The changes in c. 1835  with demolition of the northern wing and its rebuilding closer to the southern and rebuilding of the porch in between plus siting in 1881 of the Reading Room.
The Latin inscription above the porch “Parva sed apta domino l673” announced the house to be small but fit for a lord. By the second half of the 1830s it was smaller still and without a lord but from 1839 served the Lord as a vicarage for over a century.
In 1881 the Reading Room was built where the north wing had been.
It was no great surprise that the foundations of the north wing were rediscovered in 2010 when the Reading Room floor had four holes dug for girders to support a new roof. 
To let notices  in the press give an idea of the accommodation available before the alterations.
From The Salisbury and Winchester and General Advertiser of Wilts, Hants, Dorset and Somerset, Monday, June 28, 1830
To be let Mawarden Court House situate in the pleasant village of Stratford Sub-Castle, near Salisbury: containing 2 good parlours, drawing room, 9 bed-rooms, 2 kitchens, cellar, large garden, a three-stall stable, and coach house.
Also, to be let, A COTTAGE nearly adjoining the above, containing a parlour, kitchen, 4 bedrooms, cellars, and brew-house, a stable, wood house and garden. Possession of Mawarden House may be had Michaelmas next, and of the cottage, immediately.
For particulars applied to Mr Waters, Stratford, if by letter, post-paid.
NB the above premises are situate near the church; and pack of harriers are kept in the village, and the post passes morning and evening.
From The Salisbury and Winchester and General Advertiser of Wilts, Hants, Dorset and Somerset, Monday, October 22, 1832.
To be let MAWARDEN COURT HOUSE, situate in the pleasant village of Stratford-sub-castle, near Salisbury: containing two good parlours, drawing room, nine bedrooms, two kitchens, cellar, large garden, a three-stalled stable and coach-house. The above premises are now in the occupation of the Rev. R.M. Chatfield. Possession may be had immediately. ---For particulars apply to Mr Waters Stratford; if by letter post-paid.
 Ground floor plan taken from 'Stratford-sub-Castle', in Ancient and Historical Monuments in the City of Salisbury (London, 1977), pp. 164-167. British History Online http://www.british-history.ac.uk/rchme/salisbury/pp164-167 [accessed 8 November 2021]. Colour added by author
 James, David 2011. Archaeology and History Underneath the Reading Room. The Friends of St Lawrence Newsletter Issue 15 Spring 2011.
 Both to let notices, 1830 and 1832, reproduced within the terms of the British Newspaper Archive. ©The British Library Board, all rights reserved.
Reproduction of the 1805 John Buckler view of Mawarden Court from the South East is by kind permission of the ©Wiltshire Museum, Devizes.
Other pages on this website about Mawarden Court: