Originally Mac Oistigain and sometimes if incorrectly Mac Costagain, and later in the 17th century Mac Costigan, Costegan, Costigan, and even O' Costigan, this is an early Irish surname. It is however arguably Norman in origin with Oistigin being a Gaelic form of the personal name Roger. This was introduced into Ireland after the conquest of the country in 1170 by Strongbow, earl of Pembroke. The surname was once very popular in Counties Leix formerly Queens County, and Kildare, but after the battle of the Boyne in 1690 when the main clan from Grange, County Leix, supported the Catholic King James 11nd and lost, they were dispossessed and gradually lost influence. Perhaps the earliest proven recording is that of Patrick MacCostykyn as spelt of Naas, a juror in the year 1540. Later spellings include Donal MacCostigane of Queens County in 1562, and John MacCostygyn, the rector of Durrow in 1566. It seems that for a time the spelling was also given as O' Costigan as in the case of Dermot O' Costigan, who in a deposition was given as being a gentlemen "tory."