Idle Hour

William Kissam Vanderbilt, a grandson of Commodore Cornelius Vanderbilt, assembled a 900-acre estate along the Connetquot River in Oakdale. With his wife Alva he built a first country house there to designs by Richard Morris Hunt, whose drawings for it date from about 1880. In 1899 fire destroyed that house.

Vanderbilt rebuilt at once. Richard Howland Hunt, a son of Richard Morris Hunt, prepared the drawings for the new house in 1900 and 1901, and the firms of Hunt and Hunt and of Warren and Wetmore designed many of the estate's buildings. The new mansion, of brick and stone, had 110 rooms, including 45 bathrooms, and Fire Island News puts its construction and furnishing cost at more than $3 million in 1901.

Vanderbilt died in 1920, and the estate was broken up. The mansion passed through a series of owners and tenants. Fire Island News reports that the gangster Dutch Schultz rented it during Prohibition and that the occultist James Bernard Schafer acquired it in the 1930s, followed by the National Dairy Institute. Adelphi College bought the estate in 1963, and in 1968 its Oakdale branch became Dowling College. A fire in 1974 damaged the mansion, which the college repaired and later converted largely to classrooms and offices.

Dowling College lost its accreditation and closed in 2016, and its Oakdale campus was sold in a bankruptcy auction the following year. A 2017 report named the winning bidder as Princeton Education Center LLC at $26.5 million, but later reporting and a 2024 state environmental permit name Mercury International LLC as the owner. The campus has stood empty since. In 2020 Suffolk County officials said the owner owed about $4 million in property taxes, and in 2021 residents described almost nightly vandalism, stolen copper and damaged stained glass and woodwork. The Town of Islip placed the mansion, powerhouse, well and an old tree in a Planned Landmark Preservation Overlay District in 2018, and Suffolk County sent a letter of interest in buying the property in 2023 without a reply. The property is not on the National Register of Historic Places.

In 2025 neighbors arranged for Suffolk County police SWAT and K-9 units to train in the buildings, and a new property manager cleaned up some of the damage. In April 2026 the campus, eight buildings on a 25-acre waterfront tract, was offered for sale again, with bids due June 30. The mansion is closed to the public, but it can be seen across the river from Bayard Cutting Arboretum.