When I started doing Irish genealogical research thirty-odd years ago, I stumbled across A Census of Ireland circa 1659 (ed. Séamus Pender, Irish Manuscripts Commission, 1939) in the National Library reading room and my heart leapt. A published census? From 1659? Hallellujah!
But of course Pender’s Census is nothing like a census. (The decision to give it that name was not Pender’s: the manuscript in the Royal Irish Academy had been known as a ‘census’ since the mid-nineteenth century. So forgive him.)

Two classes of people are recorded. The first, ‘tituladoes’, are so called because they claim title to the land they occupy and because that title is in question. The OED defines titulado as “A thing that has only a nominal existence.” Their names and townland addresses are given in full. Because they represent the tiny property-owning class, their numbers are few.
More interesting is the second class, “Inhabitants”. These are described as English, Scotch or Irish, their surname (or a rough version of their surname) is supplied, along with their number. These numbers are for baronies, so the areas they cover are much larger than for the tituladoes.
Clearly, the ‘Census’ was part of the preparatory work for the mass confiscations that took place under the Cromwellian Commonwealth. Although the returns differ in format from one part of Ireland to another, they were designed to answer two simple questions: Who is in possession of the land? (the tituladoes) And who is likely to oppose or support their dispossession? (Numbers of English, Scotch or Irish)
Even on its own terms, the ‘Census’ is flawed. It is missing all of counties Cavan, Galway, Mayo, Tyrone and Wicklow, most of Meath (nine baronies) and four baronies in Cork. The Inhabitants of Fermanagh and Leitrim are recorded in composite groups of parishes, not baronies as elsewhere. And the recording of surnames is inconsistent beyond belief.
This much said, Pender’s ‘Census’ has one unassailable virtue: It exists. Almost no other records survive for the Ireland of this period.
The 1939 edition is available online at the IMC website. An updated version with more modern analysis by William J. Smyth, was published by the IMC in 2002. A good plain transcription, lacking the academic apparatus, is at the Clann O’Lochlainn website.
All of which finally brings me to the point for this post. I’ve spent the past few months extracting the Inhabitants’ surnames and the corresponding baronies to produce maps showing surname distribution and numbers in the mid-seventeenth century, now part of the surname search. Have a look at Whelan, for example.
Making the maps produced a little queasiness, I have to say. They do show just how long-lived is the connection in Ireland between particular surnames and places, but their implied pinpoint precision is very misleading. Treat them with caution.