Thanks for your message. A John Rattigan was born to Pat Rhatigan and Anne Tierney in Gortnagoyne in 1913, which might explain why he can't be found in the census - see https://civilrecords.irishgenealogy.ie/churchrecords/images/birth_returns/births_1913/01448/1592367.pdf. The family were living with Anne's parents in Gortnagoyne in 1911: http://census.nationalarchives.ie/pages/1911/Galway/Dunmore__North/Gortnagoyne/475202/.
I hope this might be of some help; please feel free to ask if you have any other specific questions.
IrelandXO Network Leader.