Thomas St Lawrence, 3rd Earl of Howth

Thomas St Lawrence, 3rd Earl of Howth KP (16 August 1803 – 4 February 1874) was an Irish peer, styled Viscount St Lawrence until 1822.

He became Earl of Howth in 1822 on the death of his father, William St Lawrence, 2nd Earl of Howth. He was Vice-Admiral of the Coast of Leinster, and was appointed a Knight of the Order of St Patrick on 22 July 1835 and Lord Lieutenant of County Dublin in 1851.

On 9 January 1826, he married Lady Emily, daughter of John de Burgh, 13th Earl of Clanricarde. She died of measles in 1842 in Dublin. On 27 February 1851, he married Henrietta Elizabeth Digby Barfoot (d. 5 March 1884). When he died in the south of France in 1874, he was succeeded by his son by his first marriage, William.