The park and manor house, The Farms, are attributed to owner Robert Allerton, industrialist heir, artist, art collector and garden designer.

It has been described as "a vast prairie turned into a personal fantasy land of neoclassical statues, Far Eastern art, and huge European-style gardens surrounding a Georgian-Revival mansion".

Throughout the next forty–seven years Robert Allerton transformed the country house, The Farms, into a central Illinois showplace estate, with activity climaxing in the 1920s and early 1930s.

In 1932 John Gregg (1899–1986), who would become Robert Allerton's legally adopted son in 1960, was employed full time to design new gardens and interior features in the house and help with the farm management.

Gregg had been working for Chicago society architect David Adler (1882–1949) until the effects of the stock market crash in 1929 caused a drop in house design commissions.

The commission finished its work by October 1922 with the completion of the plan for the area south of the Auditorium by Charles A. Platt (1861–1933) and was discharged at that time.

A later Illinois Supreme Court ruling resolved the matter: the university would make an annual payment in lieu of taxes to Piatt County.

New walkways, including an ADA wheelchair ramp, were installed, along with new plants, flowers, espaliered apple trees, and other landscape elements.

This garden was defined by towering arborvitae trees and annual flowers in triangular hedge parterre patterns in recent years.

In spring 2019 the garden was cleared of vegetation and replanted with new arborvitae and boxwood hedges to bring it more in scale with Robert Allerton's original design.

On the gateposts at the east and west ends are two stone animal sculptures called Assyrian Lions patterned after an ancient prototype.

[25] Located adjacent to the meadow, the Annual Garden is characterized by its colorful flower beds and the Marble Faun statue at the east end.

[28][29] Characterized by its golden Buddha statues, this structure is a two-story folly, the upper floor being an observation deck for the Fu Dog Garden.

The lower part is an octagonal concrete tower built in 1917 that houses two gilded teakwood Buddhas from Thailand and a limestone sculpture of Hari-Hara, a Brahmin god.

In summer 2007, extensive repairs were made to the tower, including restoration of the roof, and removal of the windows, which were not original to the building.

The sculpture walk concludes with The Sun Singer, a copy of an Art Moderne bronze sculpted by Swedish artist Carl Milles (1875–1955) in 1919 to stand overlooking the harbor in Stockholm.

After the statue arrived John Gregg Allerton designed a three−tiered platform styled after the Altar of Heaven in the Forbidden City of Beijing as a base in 1932.

[34][35] Located in the forest past the formal gardens, this statue by the French artist Emile-Antoine Bourdelle (1861–1929) is of an allegorical scene, the death of Paganism.

In 1965 a granite boulder with the inscription "ROBERT ALLERTON HE GAVE HIS WOODLAND HOME TO THE UNIVERSITY OF ILLINOIS FOR THE PEOPLE TO ENJOY AND TO ENRICH THEIR LIVES" was installed in the pond to commemorate his life.

[38] Two brick columns topped with statues of the goddess Diana and her companion, an Ephebe, were placed at the southeast gate on Allerton Road.

[42] In recent years, the house has been opened up for more events and is available to guests for overnight lodging as part of the Allerton Park Master Plan approved by the University of Illinois Board of Trustees in 2015.

The Gallery spans the entire length of the main house (excepting the servants' wing) and is approximately 90 feet long with a 14 ft ceiling height.

Originally called the Music Room on the architect's drawings, the Library is two stories tall and features a parquet patterned floor.

The stable facade facing the Library Terrace has two carved Indiana limestone masks designed by John Borie and located above the arched doorways leading out of a former conservatory area now called the Breakfast Room.

These are known as the Masks of Pan, and are a variation of the European Green Man, a benevolent woodland spirit carved onto many cathedrals and public buildings.

[50] Designed by Joseph Corson Llewellyn (1855-1932), this house was constructed in 1917 not of wood, the most common building material, but instead of hollow tile and blue-gray stucco.

[10] Architect John Borie designed this Colonial Revival style brick house built in 1903 as the residence of the head gardener.

After several years as an Environmental Learning Center the circa 1890 Dutch style horse barn on the property was remodeled in 2005 into a music performance venue seating 175 in the hayloft.

Allerton Park was the venue for the Symposium on Principles of Self-Organization 8–9 June 1961 organised by Heinz von Foerster through the Biological Computer Laboratory based at University of Illinois at Urbana-Champaign.

[62] The massive central Illinois Valentine's Day ice storm struck Allerton Park on 14 February 1990, resulting in much damage and a four-day power outage.