Frederick John William Lambart, 8th Earl of the County of Cavan (30 December 1815 — 16 December 1887) was a British aristocrat. He was the son of George Frederick Augustus Lambart, Viscount Kilcoursie and Sarah Coppin.
His father, while with the Coldstream Guards, was severely wounded during the Peninsular War in the battle of Talavera and remained lame for the rest of his life until his death in 1828 at the age of 39. Frederick was left an orphan. He was sent to Eton from 1829 until 1833, where he was known, without his title, simply as Lambart. The Rev. Dr Hawtrey was the then-headmaster and gave encouraging influence, which helped him succeed in his education.
He was born on 30 December 1815 at his parents' home of Ower Cottage, Fawley, Hampshire, England.