The first hard evidence of mobility comes from the early attempts to enumerate the population and produce accurate maps of Ireland, made in the 1650s by Sir William Petty[https://en.wikipedia.org/wiki/William_Petty]. In this survey are first found some clusters of O'Boyles living outside their traditional homeland. The motivation behind these surveys was not just statistical but was part of the process of identifying the native Irish and Catholic ‘Old English’ holders of land to be confiscated following the Cromwellian wars.

 

(Petty consistently uses the name 'O'Boyle' to refer to Gaelic landholders. Where 'Boyle' occurs in his account, it invariably refers to people of English or Scottish descent).

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Other lists of those liable to pay taxes (e.g. the Hearth Money Rolls) were also compiled about this time. These documents can give us some indication of the movement of people, as names crop up in areas beyond their traditional homelands but they cannot tell us much about how many of them there were.

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Petty’s Census[1] is not actually a true census, but rather a listing of landholders and adults liable to pay tax in those counties where land and property was subject to confiscation due to the Cromwellian wars.  

 

It’s difficult to know exactly who Petty was counting; having enumerated the number of ‘Irish papists’ and ‘English or Scottish protestants’ for each townland in a barony, he summarises the ‘principal Irish names’ within each barony. For example, in the barony of Boylagh & Banagh there are 1,556 ‘Irish Papists’. He provides a list of 33 ‘principal Irish names’, presumably the most frequently occurring, but these only account for 170 of the 1,556.

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Who are the remainder? Are the 170 just the landholders, or heads of households? Forty-one of these are O’Boyles, second numerically only to Gallaghers in this barony, but still not many in what is their long-term homeland.  For the county of Donegal as a whole, O’Boyles account for eighty-two (4%) of the 2,072 ‘principal Irish names’ out of a total estimated population of the county of 12,001.

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Petty’s calculation of a total population of Ireland at about half-a-million is a significant underestimate, as he was not interested in counting the landless peasants who couldn’t pay tax. There were significant fluctuations in actual population at that time, and as noted by one authority, “there is little prospect of progressing beyond informed guesswork” with respect to 17th century population figures[Cullen, 1975], but it was probably over a million[2]. Assuming the ‘true’ population of Donegal was about 25,000, of whom 4% were O’Boyles, then the number of O’Boyles in Donegal at this time might have been something in the region of 1,000 people; a wild guess but maybe not far off the mark.

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[1] Also known as Pender’s Census after Seamus Pender who edited the original in the 1930s.

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[2]It is believed that the nine counties of Ulster may have had about 300,000 people in the late 1500s before the Nine Years’ War. The war and accompanying famine, disease and migration may have reduced this by up to 50%. There are many contemporary reports of the near-empty land after Chichester’s scorched-earth policy. While there was some recovery in the early 17th century (and the influx of Scottish and English settlers) the wars of the 1640s and 50s reduced it again. Cromwell’s campaign of 1649-53 alone is estimated to have had a 20% mortality rate.  (Farrell (2017) pp75-76, note 45 p.89).