Apethorpe Hall is a very extensive building of many periods, arranged around three courtyards. The most important parts of the building form the principal courtyard, which is entered by the late 15th century North Gatehouse. The Great Hall on the west side of the courtyard also dates from this early period.
The South and East Ranges, containing the state rooms, were rebuilt in 1622-4. The South Range was re-fronted in the 1740s in Palladian style, probably to the designs of Roger Morris. A much more extensive scheme was planned at this time, but further work was limited to the rebuilding of part of the North Range to form a library. In the mid-19th and early 20th century the open arcades to the ground floor of the East Range were enclosed, together with major internal alterations here.
The state apartment is approached by the White Stair, remodelled in the 1740s. These state rooms, all on the first floor, contain an exceptional sequence of interiors from the 1620s. There are extensive decorative plasterwork ceilings and a fine series of fireplaces, of classical design and rich with figurative carving.
The Long Gallery takes up most of the length of the East Range and preserves its Jacobean oak panelling. Integral to the 1620s design of the East Range is a roof-walk, which allowed views over the park. The impressive East Front, which became the main entrance, looks out over a formal courtyard added by Blomfield in the early 20th century.
The service courtyard, to the west of the principal courtyard, contains the kitchen, a service range of c.1480 and the Orangery, added in 1718. Further west again lies the back courtyard.
There are extensive formal gardens to the south of the house, with lawns, terraces and topiary added by Blomfield, but overlain on a much earlier plan with a yew avenue and giant cedar tree.
To the north of the house lie the stable courtyard and a fine 18th century circular dovecote, though modern development during the school period has had a damaging effect. The original approach to the hall was past the church and stable court, but this was lost in 1949, with the access route now confined to the former back entrance.