The small clan of O’hAmhsaigh (O’Hampsey) had become O'Hamson by 1659, when it is recorded in the census of 1659 as one of the principal Irish surnames in the barony of Keenaght, and as O'Hampson and Hampson it is found in the contemporary Hearth Money Rolls for County Londonderry.
Amhsach’ is a byname meaning ‘mercenary soldier’ or ‘messenger’, and derives from the Old Irish adjective amhasach ‘aggressive’.
There is a pedigree of Hampson of County Cavan in the Genealogical Office which indicates that this family was of Irish origin.
To wit: "The English surname HAMPSON is of patronymic origin, and simple means 'Son of Hamon' [or Haman], with the letter "p" being intrusive as in the case of Thompson.
Its diminutives - Hamelot, Hamonet and Hameline surviving into the 18th Century as a Baptismal name, Hamon having lapsed by then into oblivion.