De Siún
de SIÚN—XII—Yonge, Younge, Young; Norman 'le Jeune,' 'le Jouen,' i.e., the young, in the sense of the younger, junior, as opposed to senior. Families of this name settled about the time of the Anglo-Norman invasion in Dublin, Kildare, and other parts of Ireland. Young of Youngstown was one of the principal gentlemen of Co. Kildare in 1598, while at the same time Young of Gareston was one of the 'men of name' in Co. Dublin.
Alphabetical Index to Irish Surnames