Plans for two more pavilions (as the two smaller blocks are known), of identical size and similar appearance, were never executed. These further wings were intended to contain, in the south-east a music room, and in the southwest a conservatory and chapel. Externally these latter pavilions would have differed from their northern counterparts by large glazed Serlian windows on the piano nobile of their southern facades. Here the blocks were to appear as of two floors only; a mezzanine was to have been disguised in the north of the music room block. The linking galleries here were also to contain larger windows, than on the north, and niches containing classical statuary.

The north front, approximately 117 yards in length, is Palladian in character, dominated by a massive, six-columned Corinthian portico; however, the south front is pure neoclassical Robert Adam. This garden facade is divided into three distinct sets of bays; the central section is a four-columned, blind triumphal arch based on the Arch of Constantine in Rome containing one large, pedimented glass door reached from the rusticated ground floor by an external, curved double staircase. Above the door, at second-floor height, are stone garlands and medallions in relief. The four Corinthian columns are topped by classical statues. This whole centre section of the facade is crowned by a low dome visible only from a distance. Flanking the central section are two identical wings on three floors, each three windows wide, the windows of the first-floor piano nobile being the tallest. Adam's design for this facade contains huge "movement" and has a delicate almost fragile quality. The neoclassical interior of the house was designed by Adam to be no less impressive than the exterior.

Hall

Entering the house through the great north portico on the piano nobile, one is confronted by the marble hall. Nikolaus Pevsner describes this as one of the most magnificent apartments of the 18th century in England. It measures 67 feet by 37 feet in plan and is 40 feet high. Twenty fluted pink Nottingham alabaster columns with Corinthian capitals support the heavily decorated, high-coved cornice. Niches in the walls contain casts of classical statuary by Matthew Brettingham the Younger and others; above the niches are grisaille panels of Homeric subjects inspired by Palladio's illustration of the Temple of Mars. The stucco in the ceiling was created by Joseph Rose in the 1770s. The floor is of inlaid Italian marble. Matthew Paine's original designs for this room intended for it to be lit by conventional windows at the northern end, but Adam, warming to the Roman theme, did away with the distracting windows and lit the whole from the roof through innovative glass skylight. The overmantels to the fireplaces are by Joseph Rose with firebaskets by Robert Adam. At Kedleston, the hall symbolises the atrium of the Roman villa and the adjoining saloon the vestibulum.

Saloon

The saloon, contained behind the triumphal arch of the south front, like the marble hall rises the full height of the house, 62 feet to the top of the dome, where it too is sky-lit through a glass oculus. Designed as a sculpture gallery, this circular room 42 feet in width was completed in 1763. The decorative theme is based on the temples of the Roman Forum with more modern inventions: in the four massive, apse-like recesses are stoves disguised as pedestals for classical urns. The paintings of ruins are by Gavin Hamilton and the grisaille panels have scenes of British worthies painted by John Biagio Rebecca. The four sets of double doors giving entry to the room have heavy pediments supported by scagliola columns, and at second-floor height, grisaille panels depict classical themes. From the saloon, the atmosphere of the 18th-century Grand Tour is continued throughout the remainder of the principal reception rooms of the piano nobile, though on a slightly more modest scale.

State bedroom

The "principal apartment", or State bedroom suite, contains fine furniture and paintings. The state bed was constructed by James Gravenor of Derby. The state bed posts are carved to represent palm tree trunks which soar up and break into flamboyant foliage at the top, sweeping in palm-fronds behind.

Drawing room

The drawing room with huge alabaster Venetian window is 44 feet by 28 feet by 28 feet. The doorcase is also alabaster. The fireplace with a scene of virtue rewarded by honour and riches is flanked by large female figures sculpted by Michael Henry Spang. The gilt sofas by John Linnell date from around 1765. They were commissioned by the 1st Baron Scarsdale and supplied, together with a second pair of sofas to Kedleston in 1765.

Dining room

The dining room, with its gigantic apse, has a ceiling that Adam based on the Domus Augustana in the Farnese Gardens. The apse contains curved tables designed by Adam in 1762 and a giant wine cooler. The ceiling contains panel paintings of the continents by Antonio Zucchi, the seasons by Gavin Hamilton and the centre is by George Morland. The original wall panels are by Francesco Zuccarelli, Frans Snyders, Claude and Giovanni Francesco Romanelli.

Music Room

The Music Room has Ionic doorcases and delicate plaster ceiling designed by Adam. The marble chimneypiece is inlaid with Blue John. The pipe organ was second hand by John Snetzler with the case designed by Robert Adam and built by Robert Gravenor. A second manual with Hautboy was added in 1824 by Alexander Buckingham. The organ was restored in 1993 by Dominic Gwynn.

Library

The library contains a Roman doric doorcase leading to the Saloon. The bookcases were designed by Robert Adam and built by James Gravenor of Derby. The plaster ceiling is divided into octagonal patterns. The library desk was built in 1764 by James Gravenor.

Other rooms

The theme carries on through the music room, down the grand staircase onto the ground floor and into the so-called "Caesar's hall". On the departure of guests, it must sometimes have been a relief to vacate this temple of culture and retreat to the relatively simple comforts of the family pavilion. Below the Rotunda is the Tetrastyle Hall, which was converted into a museum in 1927 in collaboration with the Victoria and Albert Museum in London. The kitchen is an oblong shape with a balustraded gallery at one end. This links the room to other household offices on each side.

Also displayed in the house are many curiosities pertaining to George, Lord Curzon of Kedleston, who succeeded to the house in 1916 and who had earlier served as Viceroy of India from 1899 to 1905. Lord Curzon had amassed a large collection of subcontinental and Far Eastern artefacts. Also shown is Lady Curzon's Delhi Durbar Coronation dress of 1903. Designed by Worth of Paris, it was known as the peacock dress for the many precious and semi-precious stones sewn into its fabric. These have now been replaced by imitation stones; however, the effect is no less dazzling. In addition to that described above, this great country house contains collections of art, furniture and statuary. Kedleston Hall's alternative name, The Temple of the Arts, is truly justified.

Gardens and grounds

The gardens and grounds, as they appear today, are largely the concept of Robert Adam. Adam was asked by Nathaniel Curzon in 1758 to "take in hand the deer park and pleasure grounds." The landscape gardener William Emes had begun work at Kedleston in 1756, and he continued in Curzon's employ until 1760; however, it was Adam who was the guiding influence. It was during this period that the former gardens designed by Charles Bridgeman were swept away in favour of a more natural-looking landscape. Bridgeman's canals and geometric ponds were metamorphosed into serpentine lakes.

Adam designed numerous temples and follies, many of which were never built. Those that were include the North lodge (which takes the form of a triumphal arch), the entrance lodges in the village, a bridge, cascade, and the Fishing Room. The Fishing Room is one of the most noticeable of the park's buildings. In the neoclassical style, it is sited on the edge of the upper lake and contains a plunge pool and boat house below. Some of Adam's unexecuted design for follies in the park rivalled in grandeur the house itself.

A "View Tower" designed in 1760 – 84 feet high and 50 feet wide on five floors, surmounted by a saucer dome flanked by the smaller domes of flanking towers — would have been a small neoclassical palace itself. Adam planned to transform even mundane utilitarian buildings into architectural wonders. A design for a pheasant house (a platform to provide a vantage point for the game shooting) became a domed temple, the roofs of its classical porticos providing the necessary platforms; this plan too was never completed. Among the statuary in the grounds is a Medici lion sculpture carved by Joseph Wilton on a pedestal designed by Samuel Wyatt, from around 1760–1770.

In the 1770s, George Richardson designed the hexagonal summerhouse, and in 1800 the orangery. The Long Walk was laid out in 1760 and planted with flowering shrubs and ornamental trees. In 1763, it was reported that Lord Scarsdale had given his gardener a seed from a rare and scarce Italian shrub, the "Rodo Dendrone" (sic). The gardens and grounds today, over two hundred years later, remain mostly unaltered. Parts of the park are designated as a Site of Special Scientific Interest, primarily because of the "rich and diverse deadwood invertebrate fauna" inhabiting its ancient trees.