Recorded in several spelling forms including MacGilmartin, McGilmartin, Gilmartin, Kilmartin and sometimes Martin, this is an Irish surname. It derives from the pre 10th century "Mac Giolla Mhartain", meaning the follower (giolla) of St. Martin, an early saint. The sept is a branch of the O'Neills of Fermanagh and Tyrone, being chiefs in the barony of Clogher, in County Tyrone. Those that moved into Connacht became Kilmartin. When combined together in all the spellings this surname is among the fifty most numerous names in Ireland. At the time of Petty's Census of Ireland in 1659, the Gilmartus and Kilmartins were moving to the territory where they are now chiefly found in Counties Leitrim and Sligo. Early examples of the surname recording include those of Feargal Mac Martin, the bishop of Killala, who died in 1431, whilst Michael Kilmartin married Margaret Heavy at Ballyhay, Cork, Ireland on April 3rd 1780. Mary Gilmartin was one of the earliest emigrants to flee the infamous Potato Famine. Aged tenty one, she left on the ship Cornet of Liverpool for New York on May 18th 1846, whilst George Kilmartin, given as being a gardener, left London for New York aboard the ship "Ellen" on April 28th 1847. The first recorded spelling of the family name is shown to be that of Giolla Earnain O'Martin. He was described as being the chief brehon or professor of law in Ireland. This was dated 1231, during the reign of Hugh "Caobhdhearg" or Red Hand, High King of Ireland, circa 1224. Throughout the centuries, surnames in every country have continued to "develop" often leading to astonishing variants of the original spelling.