ɐkˈoːɹdɪŋ tə ðə hɪstˈoːɹiən sˈiː. tˈɑːməs kˈɛɹni, ðɪ oʊfˈæɹəlz wɜː pˈɑːɹt ʌvðə kˈɑːnmeɪkni ɹˈeɪn tɹˈaɪb ɪn ˈaɪɚlənd hˌuː kˈeɪm fɹʌmðɪ ɪɹˈeɪn tɹˈaɪb hˌuː wɜː ðə sˈɛkənd wˈeɪv ʌv kˈɛlts tə sˈɛɾəl ɪn ˈaɪɚlənd fɹʌm ɐbˌaʊt fˈaɪvhˈʌndɹɪd ænd wˈʌnhˈʌndɹɪd bˌiːsˈiː.
According to the historian C. Thomas Cairney, the O'Farrells were part of the Conmaicne Rein tribe in Ireland who came from the Erainn tribe who were the second wave of Celts to settle in Ireland from about 500 and 100 BC.