Authors
- Frank O'Gorman
- Mervyn O'Gorman 1
- R. O'Gorman
- Richard O'Gorman
- Jane O'Grady
- K.T. O'Grady 1
- Rohan O'Grady
- Micheal O'Guiheen
- Andrew O'Hagan
- Hans C. O'Hanian
- C. O'Hanlon
- Mark O'Hanlon 1
- Redmond O'Hanlon 1
- Thomas J. O'Hanlon
- C.W. O'Hara
- G. O'Hara
- George C. O'Hara
- John O'Hara
- Kane O'Hara 1
- Marjorie O'Hara
- Mary O'Hara
- Vincent P. O'Hara
- Colette O'Hare 2
- P.A. O'Hare
- Cleophas C. O'Harra 1
- Pixie O'Harris
- Anthony O'Hear
- James O'Heare
- Nila O'Hearn
- Finola O'Kane
- Bernard J. O'Keefe
- James O'Keefe 1
- Michael O'Keefe
- Paul O'Keefe
- Tadhg O'Keefe
- Adelaide O'Keeffe 1
- Eamonn O'Keeffe
- Georgia O'Keeffe
- Madge Cusack O'Keeffe
- Paul O'Keeffe 1
- Bernard O'Kelly
- Claire O'Kelly
- Denis O'Kelly
- Donal O'Kelly
- Michael J. O'Kelly
- Sebastian O'Kelly
- Elizabeth O'Kiely 1
- Barrie O'Leary
- De Lacy O'Leary
- Galbraith O'Leary
- Helen O'Leary
- James L. O'Leary
- John G. O'Leary
- Michael O'Leary 3
- Mick O'Leary
- Mike O'Leary
- Paul O'Leary
- John O'London
- B.M.E. O'Mahoney
- Charles O'Mahony
- Patrick O'Mahony
- Tony O'Mahony 1
- Michael B. O'Mainnin
- Brendan O'Malley
- Brian O'Malley
- J.J. O'Malley
- Jeanne O'Malley
- Kevin O'Malley
- Mary O'Malley
- Owed O'Mally
- Lesley O'Mara
- Michael O'Mara
- Robert O'Meally
- Barry E. O'Meara
- O.T. O'Meara
- Debbie Trafton O'Neal
- Hank O'Neal
- B.H. St. J. O'Neil
- Dennis O'Neil
- Denny O'Neil
- Elizabeth O'Neil
- J. O'Neil
- Jackie O'Neil
- Jacqueline O'Neil
- Paul O'Neil
- Peter V. O'Neil
- William J. O'Neil
- O'Neill
- Amanda O'Neill
- B.H. St. O'Neill
- Barrett O'Neill
- Brian D. O'Neill
- Dan O'Neill
- Daniel O'Neill
- Desmond O'Neill
- Eamonn O'Neill
- Elizabeth O'Neill
- Eugene O'Neill
- Eugene G. O'Neill
- Gerard K. O'Neill