In 1930, Ann Borodell Denison Gates, affectionately known as Aunt Annie, created the George and Ann Borodell Denison Society. Being the last Denison to live in the house, she gave the Society the 1717 house (known as Pequotsepos Manor) and approximately 125 of the original 250 acres which was granted to Captain George Denison on 1654 for his service in the Pequot War. According to the Articles of Association, "The purpose is to maintain a museum and memorial in the town of Stonington, CT as a testimonial to the Denison Family."
In 1946, the name was officially changed to The Denison Society and J. Frederick Kelly, the notable Colonial Revival architect, was hired to restore the house as a museum. Each of the five rooms were restored to meet a different period in history and the Denison family members that lived there at that time. Additionally, the rooms were furnished with family heirlooms.
Also in 1946, The Denison Society created the Pequotsepos Wildlife Sanctuary Inc. in honor of Ann Gates' love of birds. The Sanctuary was purposely formed as a separate organization from the society. They were given a 25 year lease and an operating subsidy of $1.00 a year.
In 1972, the Denison Pequotsepos Nature Center, DPNC, was incorporated due to the generosity of the The Denison Society. Today, while The Denison Society owns all the land and buildings, DPNC leases 77 acres on the east side of Pequotsepos Road for a very generous $1.00 per year. In addition, the DPNC maintains 8 miles of trails across the Homestead property. Each group operates as a separate non profit organization with 3 members of The Denison Society Board of Trustees sitting on the DPNC's board.
In 1979, the Denison Homestead was placed on the National Register of Historical Places.
In 1992, The Denison Fund was launched by the Society to purchase 50 acres below Pequotsepos Manor. The land was owned by family member Dr. Walter Morgan. This land was part of the original 250 acre land grant given to Captain George Denison. Bill Denison was instrumental in a capital campaign to buy this property and to stop a proposed development only a few hundred feet from the 1717 house.