The Forty Hall Visitor Book contains details of the many visitors who stayed at Forty Hall between January 1938 and September 1951. They include Mary de Trafford Bowes-Lyon and her husband Francis, who were Ann Parker Bowles' sister and brother-in-law. Ann Spencer Churchill, Mrs Parker Bowles' cousin also visited the house, as did Kathleem (Kick) Kennedy, daughter of US Ambassador Joseph Kennedy and sister of US Presidents John and Robert Kennedy.