William Handcock 28 August 1761 – 7 January 1839 1st Viscount Castlemaine, Baron Castlemaine

Created 1st Baron Castlemaine on 21 December 1812. Handcock had no children, so that the peerage was created with a special remainder "failing heirs of his body to his brother" so that his brother would succeed William Handcock as the second baron.

Created 1st (and last) Viscount Castlemaine on 12 January 1822 but no such remainder was given, and the Viscountcy became extinct.

Constable and Governor of Athlone 1813–39 and Governor of County Westmeath 1814–31;

Both peerages were Irish and so Handcock never sat in the British House of Lords