1. Joseph F. O'Callaghan's The O'Callaghan Family of County Cork: A History This excellent book is a history of the Callahan family written by Joseph F. O'Callaghan, an academic historian, and represents a lifetime of research.
As of January 2017, the book can still be obtained as it is "published on demand" from a printer in Ireland. The book originally came out in hardback at $70 (plus some for shipping) when I bought it years ago, but it was a limited run.
Here's the info I just received about the reprints.
"We can re-print and bind “The O Callaghan Family of County Cork, A History”
@€60 per copy
Kind regards,
Caroline Redmond
Kennys Bindery
13-18 Kilkerrin Park,
Liosbán Industrial Estate,
Tuam Road,
Galway,
Ireland.
Mobile: +353 (0)87 1300 656
+353 (0)87 1208 147
Phone: +353 (0)91 756 737
Fax: +353 (0)91 757 516
Email: bindery@kennys.ie
Website: www.kennysbindery.ie "
2. The Irish Saga about the First Callahan in the 10th Century Caithreim Ceallachain Caisil(the progenitor from whence the surname derives). Click on this link for a .PDF copy.
3. Herbert Webb Gillman's extensive journal article about Callahan genealogy and history: The Chieftains of Pobul-I-Callaghan, County Cork, Journal of the Cork Historical and Archaeological Society Vol. III, June 1897 (p. 201, 205-206). This journal issue is also available as a free E-book on Google Books. It describes the genealogy of the O'Callaghan clan and their later history. The book is available to be read on this website at the bottom of the Photos of Callahan Castles webpage.
4. Historical and Topographical Notes: Clonmeen Parish. Click on the PDF link below for a copy.
5. Historical and Topographical Notes: Dromaneen Castle. Click on the PDF link below for a copy.