Cornelius O'Callaghan, 1st Viscount Lismore

Cornelius O'Callaghan, 1st Viscount Lismore PC (I) (2 October 1775 – 30 May 1857) was an Irish Whig On 30 May 1806 he was created Viscount Lismore in the Peerage of Ireland.

From 1806 to 1807 he sat in the House of Commons of the United Kingdom as a Member of Parliament (MP) for Lostwithiel, a rotten borough in Cornwall controlled by Lord Mount Edgcumbe.

In 1835 he was made a Member of the Privy Council of Ireland. In 1838 he was made Baron Lismore in the Peerage of the United Kingdom, giving him and his descendants an automatic seat in the British House of Lords. He served as Lord Lieutenant of Tipperary between 20 October 1851 and his death in 1857.

He married Lady Eleanor Butler, daughter of John Butler, 17th Earl of Ormonde and Lady Frances Susan Elizabeth Wandesford, on 11 August 1808. They divorced in 1826. He was succeeded in his title by his third and only surviving son, George O'Callaghan.

The 1st Viscount of Lismores son Cornelius O'Callaghan (1809–1849) who pre-deceased him, served as MP for Tipperary and Dungarvan in the House of Commons.