[4] The current building replaced an earlier mansion, also called Killenworth, which was constructed for Pratt around 1897 by William Tubby, with landscaping by the Olmsted Brothers.

[7][8] The presence of the Russians made the property the target of demonstrations, requiring the City of Glen Cove to provide additional police protection that was not reimbursed.

[7] When Soviet leader Nikita Khrushchev visited Killenworth in 1960, crowds reportedly threw tomatoes at his party's limousines.

[7][11] In the 1980s the facility was subject to allegations that it was being used for espionage, with defector Arkady Shevchenko stating that its top floors were occupied by equipment for signals intelligence.

It was initially reported that Killenworth might be the Long Island site,[14] but the designated facility turned out to be another mansion owned by the Russians called Norwich House[15] in nearby Upper Brookville, New York.