The Gleason name is documented in the the "Genealogy of descendants of Thomas Gleason of Watertown Mass."By John Barber White,1909.Ten generations are covered in the book. 1607-1909. The Gleeson/Irish-Ui Glasain or Ui Gliasain-were a native Irish Sept/Family branch-who had their original native Irish territory in Tipperary Co.in the Irish Kingdom of Ormond/Alumumu-under the control of the Dal Gcais Tuaths of the O'Kennedys and O'Mearas.In Kerry Co.they anglicised their name as O'Glissane. As to the Leesons they came into Ireland in the 17th Century,but there was a native IRISH Sept who anglicised as O'Lishane which was a corrupt form from O'Gliasain. This is were the confusion occurred from the "Leeson-Gleason"English Line John Barber White 1909 wrote about.