Some statistics and statistical conclusions taken from “Varities & Synonymes of Surnames and Christian Names in Ireland” By Robert Matheson, Secretary of the General Register Office, 1894

       Surnames of Ireland, Robert Matheson, 1890 Birth Records
In 1890 the average birth rate for Ireland was 1: 44.8
Therefore based on the figures above the population of Gallaghers in Ireland in 1890 is reckoned to be 21,862.