The name Crumlin occurs frequently in the local nomenclature of Ireland, and in an Irish poem entitled "The Battle of Gabrha" it is mentioned as being the residence of the Fenian hero Ossian. This poem has been published in the Transactions of the Ossianic Society and the editor gives the meaning of the word Crumlin as the "the lake of Crom" (or Crum), who was a pagan deity who received the offerings of the husbandmen for the fruits of the earth. More modern thinking would prefer the derivation of Crumlin as being from the Irish "Cruimghlinn", meaning the curved or crooked glen, of which the present Lansdowne Valley is the original in this instance. Drimnagh Castle guards the southern end together with, further to the eastern fortified tower of Crumlin Church. Early Bronze Age graves and cemeteries dating from 2000— 1200 B.C., and incorporated in custom built cairns of stone, attest to the extreme antiquity of the area. The urns, human remains and other finds from the excavated tombs are deposited in the National Museum.
There would appear to have been a church in Crumlin from the twelfth century, since in 1169 William de Harptre (Harptree) was possessed of the advowson of Crumlin. The O'Tooles, after their raid on Tallaght in 1331, ambushed a number of leading inhabitants of the neighbourhood who were pursuing the raiders and not sheltering in Crumlin Castle which the Crown had erected some years before for the protection of the populace.
Some years later in 1337 the King granted to the natives and tenants of Crumlin 122 acres of land provided they, and their heirs, within ten years, and at their own expense, caused the town to be enclosed against the attacks of enemies. There were several small castle towers in or near the village of Crumlin in 1594, but these afforded little protection when the village was plundered and burnt by Gerald Fitzgerald, leader of the Wicklow insurgents, with some eighty followers. The raid took place at night, and the church was plundered also, the lead roofs of the church and chancel being stripped to make bullets. As soon as the village began to be rebuilt it was raided and burnt again in 1599 by Fiach MacHugh O'Byrne of Glenmalure.
In 1690, after the victory of the Boyne, King William and his army encamped in Crumlin on July 9th for two days. In the second half of the seventeenth century a portion of the Crumlin lands came into the possession of Major Joseph Deane, an officer in Cromwell's army. It is said that Captain's Road is named after him. In 1780 the antiquarian Austin Cooper visited Crumlin and recorded that it had very few houses, mostly the country retreats of citizens. St. Mary's Church was rebuilt in 1817 with the help of a loan of £1,000 from the late Board of First Fruits, the old medieval tower being preserved. The handsome classical doorcase in the west wall is an extremely fine design by a skilled architect and very probably dates to the early eighteenth century making it contemporary with the boundary wall.