A huge thanks for all your replies to this topic.
There certainly are surname distribution ‘patterns’ that emerge when exploring the settlement of Ulster by the English and Scottish during the 17th and 18th centuries and I now know that comparative studies have been made. On a quick surfing session on the net, I came across an excerpt from a book called Finding Your Irish Ancestors: Unique Aspects of Irish Genealogy (Mitchell). He reiterates that large numbers of English families settled in the southern counties of Ulster and were of predominantly northern English origin – Cheshire, Cumberland, Lancashire, Northumberland, Yorkshire and Westmoreland, and were concentrated along the Lagan Valley, whereas the Scottish arrived at Coleraine and the Foyle. He also states that the London Companies had difficulty keeping the ‘ill-prepared and ill-suited’ English planters to stay in Ulster, so that the Companies looked to the more tenacious and adaptable lowland and border Scottish to tenant their estates, obviously resulting in the high density of families in the northwest with Scottish origins.
In this book the author makes reference to the research of W. Macafee‡. The two texts he cites indicate that “the evolution of predominantly English or Scottish settlement areas in Ulster was established from the earliest days of the 17th century Plantation of Ulster” and that the marked changes in surname distribution between the 1631 muster rolls and 1666 hearth money rolls indicate “a high level of internal mobility and population turnover”. In the second manuscript Macafee examined surname distribution in south Derry over time by comparing the 1659 census, the 1663 hearth money rolls, the 1740 religious census returns and the 1831 census. He likewise concluded that after 1700, changes in protestant settlement in Ulster were the result of “internal movements of population” and not the result of further migration from Scotland and England.
The geographical area that I have been primarily interested in establishing the surname origins within is Magilligan/Tamlaghtard. There were a number of English families there from the 17th and 18th centuries, amongst them: Gage of Raunds, Northamptonshire, Lane, Reynolds, Chase, Church, Cust of Yorkshire (Henry b:1646 d:1717) and Moorhead. I think there were more English families than those mentioned here. My own family, the Leekes/Leakes, appear to be of English origin and the surname was quite widely distributed across England by the 17th century in such places as: Shropshire, Tyne and Wear, Yorkshire, Nottingham, Cambridge, Gloucester, Berkshire, Northamptonshire, Lincolnshire, Norfolk, London, Kent, Devonshire, Cornwall and elsewhere (everywhere it seems!). To date I have been unable to source any records of their being in Magilligan before 1740. Senior members of my family have claimed that the Leekes were indeed English and arrived in Magilligan sometime in the early 1700s, after the Siege of Derry. They were a 'lowly' tenant farming family who appear to have first settled in Upper Doaghs.
‡The Movement of British Settlers into Ulster During the Seventeenth Century, published in Familia, Ulster Historical Foundation, Belfast, Volume 2, Number 8, 1992
‡The Colonisation of the Maghera Region of South Derry During the Seventeenth and Eighteenth Centuries, published in Ulster Folklore, Volume 23, 1977