dont know if you know a location for the Egan's  - but here are a few Kings County/Offaly entries from Pigots Commercial Directory of 1824. (I am assuming that the mention of the 1940s is a typo...)
  Parsonstown/Birr
  John Egan , Main-street - Grocer
  John Egan , Main-street - Linen & Woolen Draper 
  Philipstown/Daingean
  Bartholomew Egan - Publican
and from Slaters 1846
  Birr
  Dennis Egan, Market square - Boot & Show Maker
  Patrick Egan, Grave yard - Culter & Gunsmith
  John Egan & Co. Main st - Grocer
  Thomas Egan , Main st - Publican
  John Egan & Co. Main st -  Seedsman
  
  Clara
  Patrick Egan -  timber merchant and  tallow chandler
  Tullamore
  Constantia Egan, Barrack st  - Bookseller (Stationer & Printer)
  David Burgess Egan, Barrack st - Bookseller (Stationer & Printer)
  Egan Michael, William st, Tullamore - Grocer
 
 
Shane