[1] In 1908, Clark built a 160-metre (520 ft) long suspension bridge over the deep gully which lies between Mt Wilga and Hornsby railway station to facilitate the arrival of guests to the property from Sydney.

Wilga, Clark had resided in "Sefton Hall" in Marrickville Road, Dulwich Hill, which was named after a property in England.

Wilga was reputedly designed by the owner and planned along similar lines to his summer home "Sefton Hall" at Mount Wilson in the northern Blue Mountains.

The large allotment containing Mt Wilga house remained in private hands until its sale in 1952 to the Commonwealth of Australia for use as a rehabilitation hospital.

[1] During the 1950s, the hospital had a major role in the founding of the Australian Paralympic movement, led by staff members John Grant, Eileen Perrottet, and Kevin Betts.

[3] In 1985, Howard Tanner & Associates (HT&A) prepared 'Mt Wilga, Hornsby NSW: Conservation Management Plan for the Administration Building' for the Commonwealth Department of Housing and Construction.

In January 1987, Howard Tanner wrote to the then Heritage & Conservation Branch advising of the impending sale of the property by the Australian Government.

In March 1987, HT&A wrote to the Heritage & Conservation Branch making recommendations for a site curtilage based on historic and contemporary conditions.

[1] Concern over the future of the site led to the placement of a Permanent Conservation Order (PCO) #535 over the house and some of the curtilage on 4 September 1987.

In their present state, the grounds reflect the reduction of the gardens and expansion of open lawn areas, the gradual attrition and simplification of planting and the removal of the majority of the trees, associated with the institutional management of the site.

[1] In August 1991, a Conservation Management Plan was prepared by Robertson & Hindmarsh Pty Ltd for Soka Gakkai International Australia, a Buddhist group who made a number of small modifications to the house and outbuildings.

These included repainting the interior and exterior of the house, carpeting, refurbishing a former minor building into a women's temple and various services were partially separated from the hospital to the north.

[1] Since 2006, one residential allotment facing Manor Road (known as Lot 2 in DP 1181742), outside the NSW State Heritage Register curtilage boundary, has been subdivided off the property.

[1] In 2015, a major renovation and extension plan was approved for the current owners with the aim of upgrading the house and grounds to a modern family residence.

This retains the core of the eastern garden, driveway and a good part of the former service area, including the tennis court, bowling green and site of the former chicken house.

Subdivision and redevelopment of the hospital to the north and west has greatly altered much of the estate's land there and encroaches fairly close to the carriage loop and western boundary of Mt.

[1] Large mature trees including Bunya Bunya pine (Araucaria bidwillii), Port Jackson or rusty fig (Ficus rubiginosa) and Monterey pines (Pinus radiata) to 20 metres (66 ft) (probably from c. 1910) camphor laurels (Cinnamomum camphora) and brush box (Lophostemon confertus) to a 16m evergreen /southern magnolia / bull bay (Magnolia grandiflora) and crepe myrtle (Lagerstroemia indica).

Along the southern boundary there is a row of turpentine trees (Syncarpia glomulifera) to 15m high which have grown since the 1950s and, further to the south-west adjoining the former service driveway to the former garage, a Himalayan cedar (Cedrus deodara), book leaf cypress/arborvitae (Platycladus orientalis) and brush box trees (now outside the boundary to the west near the former service drive).

[1] Also mature trees on site include two sweet gums (Liquidambar styraciflua), two frangipani (Plumeria rubra) flanking the front steps to the house, a rare jambos/ rose apple (Syzygium jambos) tree on the eastern boundary near the entrance drive, an ironbark tree west of the house (Eucalyptus sp., possibly E.crebra), a NZ flax bush south of the drawing room (Phormium tenax) and a large Chinese wisteria (Wisteria sinensis) on the wire mesh fence of the tennis court.

[1] Federation mansion with face brick walls, complex steep pitched terracotta tiled roof, tall roughcast chimneys, shingled and half-timbered gables, sandstone veranda piers with simple scalloped timber valences.

[1] 2007-8: 88 units with basement parking: repairs and maintenance work to preserve the fabric of the building, including the: As at 18 September 2014, outstanding late Federation Queen Anne style mansion.