Taken from "A Dictionary of Surnames" written by Patrick Hanks and Flavia
   Hodges and published by Oxford University Press.

   Grogan Irish: 1. Anglicized form of Gael. Ó Grúgáin 'descendant of Grúgán',
   a personal name from a dim. of grúg anger, fierceness.

   2. Anglicized form of Gael. Ó Grúagáin 'descendant of Gruagán', a personal
   name from a dim. of gruag hair. the patr. form Mac Gruagáin (Anglicized
   McGrogan) is much rarer. Vars.: O'Grogaine, O'Growgane, Groggan,
   Groogan.

   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

   (O) GROGAN

   The following information is taken from "More Irish Families", written by Dr.
   Edward McLysaght and published by Cambridge University Press.

   The O prefix of this name - Ó Gruagáin in Irish - was dropped in the
   seventeenth century and does not appear to have been resumed at all in recent
   times. We hear first of the sept in 1265 under the date the Four Masters and
   other annalists record the death of Maelbridghe Ó Grugáin (or Ó Grocan) of
   Elphin.

   In the sixteenth and seventeenth centuries references to the name in our
   surviving records are plentiful, but by 1550 the sept had been dispersed from
   their homeland in Connacht to an unusual degree. In the Tudor Fiants, in
   which the name appears usually as O'Grogan, but with variants such as
   O'Gruagane, O'Growgane and O'Gruogan, six of the relevant dozen relate to
   Co. Limerick, the others to Counties Kildare, Offaly and Tipperary, and only
   one is placed near the sept's original habitat. None is from Co. Westmeath, yet
   less than a century later, when Petty's census was compiled in 1659, Grogan is
   listed as one of the principal Irish surnames in the barony of Farbill in that
   county and also in the barony of Ballyboy, Co. Offaly.

   Some of the names by which these men and women were recorded are brief
   pedigrees in themselves: e.g. Molaghlin MacEe MacCoin O'Gruagan of
   Castleton, Co. Limerick, who in 1759 was with many of his neighbours fined
   20s., pardoned and ordered to find security for his peaceful behaviour.
   Katherine nyne Tyaung, alias Katherin ny Gruagaine, of Gortacleane provides
   another intriguing entry. Most of these people are described as husbandmen
   and yeomen, though we have also a horseman, a tailor and even a labourer.
   Unlike most of our earlier records the Fiants are not concerned solely with
   landholders, soldiers and politicians.

   Few townlands were named later than the early seventeenth century so that
   Ballygrogan in Co. Tipperary and Derrygrogan in Offaly, near Tullamore,
   presumably called after branches of the family, provide corroborative evidence
   of their establishment in those areas. Modern statistics also indicate their wide
   distribution in recent times: birth registrations show approximately the same
   number in three provinces with considerably fewer in Ulster: in the northern
   province the variants Groggan, Groogan and Grugan are found, the last of
   these being apparently almost peculiar to the Omagh district.

   In the seventeenth century individual references are too numerous to be
   enumerated in this brief account: we find, for example, one as a witness to the
   will of Nugent, Baron of Delvin, in 1602, another Dominican Prior of Urlagh in
   1631, another in the list of 1649 officers; and this century begins the
   authenticated pedigree of the principal landed family of the name, Grogan of
   Johnstown Castle, Co. Wexford, which is registered at the Office of Arms at
   Dublin Castle. In 1878 the Grogan estates totalled upwards of 13,000 acres in
   Counties Wexford, Wicklow, Westmeath and Offaly.

   Of this family was Cornelius Grogan (1738 - 1798) of the County Wexford
   gentry who joined the United Irishmen: he was executed for his prominent part
   in the Insurrection; his brother Thomas, who fought on the other side, was
   killed in action. Sir Edward Grogan, Bart., (1802 - 1891), who was M.P. for
   Dublin City for 25 years, was also of this family. Nathaniel Grogan (1740 -
   1807), a painter of note, was a Cork man. Click here to see one of Nat's paintings