The Down Survey, carried out between 1655 and 1656 under the direction of William Petty, was a vast administrative exercise intended to document Irish land ownership following the Cromwellian conquest, and its detailed parish maps are still among the most useful tools for locating early modern structures. On one of those maps, a house is marked at a place rendered as "Backstowne", on the very ground where Westownpark House stands today.

At the time the Down Survey recorded it, the house was occupied by Thomas Sedgrave, who belonged to a Dublin mercantile family. The Sedgraves were part of the established commercial class of the city, and their presence in this part of County Dublin reflects the pattern of merchant families acquiring rural properties in the hinterland of the capital during the sixteenth and seventeenth centuries. After the Restoration of the monarchy in 1660, the property passed into rather different hands. According to Francis Elrington Ball's 1906 account, Backweston House had by that point become the residence of Sir Bryan O'Neill, a baronet and Knight. The current building on the site is a three-bay Georgian house, a form typical of the eighteenth century, with later additions altering its original appearance somewhat.

The house is a private residence rather than a publicly accessible site, so any visit to the area is best kept to the public road and the surrounding landscape. The interest here is largely in the layering of history concentrated in a single location, from the Cromwellian survey to the post-Restoration gentry to the Georgian rebuild. Those with a particular interest in the Down Survey maps can consult digitised versions held by Trinity College Dublin, which allow the "Backstowne" notation to be viewed in its original cartographic context and compared with the modern landscape.