In 1922 Allerton met John Gregg (1899–1986), an orphan and aspiring architect, who worked for the society architect David Adler in Chicago during the 1920s. After the stock market crash of 1929 Adler′s work diminished and Gregg came to live at Allerton′s estate as landscape architect and business manager, a salaried position. Allerton and Gregg became lifelong companions. After a change in Illinois law in 1959, Allerton legally adopted Gregg as his son although Gregg didn′t adopt the Allerton name until after Robert′s death in 1964. Following Robert Allerton′s death on 22 December 1964, according to his wishes John scattered his ashes on Lawai Bay, Kauai, Hawaii. When John died on 1 May 1986 his ashes were also scattered on the bay. While, if so, they would have been closeted, it is believed that Allerton and Gregg were involved in a homosexual relationship, at a time when American society was not accepting of such relationships. Same-sex adult adoption had been a utilized by couples in the time before the legalization of same-sex marriages and unions.