Stephen Moore, the 3rd Earl Mount Cashell (20 May 1792 – 10 October 1883), known as Lord Kilworth until 1822, was an Anglo-Irish nobleman.

Born in Dublin, Ireland, he was the son of Stephen Moore, 2nd Earl Mount Cashell, and Margaret King, daughter of Robert King, 2nd Earl of Kingston. His mother, influenced by her time as a student of Mary Wollstonecraft, held progressive views on child education and treatment. He completed his education at Trinity College, Cambridge.

Lord Mount Cashell resided in Switzerland for a period and in 1819, married Anna Marie Wyse/Wyss (circa 1793-1876) of Berne. Subsequently, the couple settled in Frankfurt, Germany, and had four daughters and three sons.

Elected as an Irish Representative Peer in 1826, he secured a seat in the House of Lords.

In 1847, he became a Fellow of the Royal Society. By 1870, the family had concluded their affairs abroad and returned to Britain. In his later years, Mount Cashell, then between 85 and 90, was reportedly engaged to a Miss Kennedy. He passed away in Paddington, London, at the age of 91 in October 1883.