According to a document held by the College of Arms in London, John Cree of Ennis had a daughter Ellen Cree who married James McMahon of Ennis Co. Clare (died 1783). As far as we know their son was known as John Cree throughout his life, (although he was referred to as John MacMahon, otherwise Cree, in a document written twenty years after his death).
He made his fortune as a free merchant in the East Indies. Incidentally, although he is recorded as having died "without issue" he did in fact have two children, a son and a daughter, whose baptisms were recorded in Calcutta with the description "natural child". His only "legitimate" child died at the age of four, so his estate passed to his nephew, also John McMahon, of Thornhill in Dorset, and "by Royal Licence bearing date 1 June 1815 he [the nephew] and his issue were authorised to assume the surname of CREE only and to bear the arms of Cree pursuant to a clause in the last will and testament of his uncle John Cree abovementioned." So the nephew changed his name to Cree. He later acquired Moignes Court, also in Dorset.
Later the estate passed through a daughter to George Stone, who also had to change his name to Cree in order to inherit. Moignes Court is today occupied by his descendants who as a result of the will of the original John Cree, formerly McMahon, still bear the name Cree.
The life of John Cree has now been thoroughly researched, mainly by Trevor Cree and Mike Spathaky. His genealogy can be seen in the Cree On-line Genealogy Database on his person details page. You can also read Mike's Biography of John Cree, while a large number of transcriptions of archives relating to his life are listed in the Archives Section under the name Merchant of Dacca.
