Ynys Fawr
- mundane location: Tasmania
- formerly/alternately known as Ultima Australis
- website: http://lochac.sca.org/ynys_fawr/
- was a shire in Lochac from 22 July 1989 to 9 July 1993
- barony in Lochac since 10 July 1993
Landed Gentry of Ynys Fawr
- Hrolf Herjolfssen and Madelaine de Bourgogne
- Baron and Baroness of Ynys Fawr
- invested on 10 July 1993
- stepped down on 28 June 1997
- Gershom of Ravensdale and Miriam de Mont Noir
- Baron and Baroness of Ynys Fawr
- invested on 28 June 1997
- stepped down on 25 September 2004
- Arnfinnr Ákason and Anna Caterina del Cossa
- Baron and Baroness of Ynys Fawr
- invested on 25 September 2004
- stepped down on 2 June 2007
- Snorri Blódhdrekkr ór Ódhinslundi and Stella de Ravenscar
- Baron and Baroness of Ynys Fawr
- invested on 2 June 2007
- stepped down on 16 May 2009
- Lucas Maxwell and Madeleine de Chalôns
- Baron and Baroness of Ynys Fawr
- invested on 16 May 2009
- stepped down on 20 October 2012
- Hrolf Herjolfssen and Madelaine de Bourgogne
- Baron and Baroness of Ynys Fawr
- invested on 20 October 2012
- stepped down on 19 November 2016
- Adelindis filia Gotefridi and Anna Felice Tavestoche
- Baroness and Baroness of Ynys Fawr
- invested on 19 November 2016
- stepped down on 7 March 2020
- David de Darlington and Arabella de Darlington
- Baron and Baroness of Ynys Fawr
- invested on 7 March 2020