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All of O'Carroll's published works draw their inspiration from the history of southwest Ireland, particularly County Kerry, with particular emphasis on the 12th century Norman settlement and the later Elizabethan and seventeenth-century settlements. These interests informed his first book, the writings of Mr. Justice Robert Day, a Kerry native and Dublin-based member of the court of King's Bench. He next undertook the writing of a history of Tralee. Recognising the need for such a publication, he made contact with Sir Anthony Denny, who was descended from the leading Elizabethan planter of the region, who placed important archive material at his disposal. The resulting book revealed the restrictive town charter of pre-democratic days, but assessed the positive contributions of settler representatives- Blennerhassett, Rowan and Denny included.
O'Carroll's book on the Geraldine earls of Desmond, published in 2013, was the culmination of over thirty years of interest in the subject. Like his previous books, it drew its inspiration from the fact of historical continuity: despite war, including the occasional massacre in Elizabethan and Cromwellian times, by the nineteenth century the blood of the Geraldine earls was running in the veins of some of the settler families who composed the regional elite. This awareness had been forgotten by historians working within the confines of recent nationalism. O'Carroll lives in Limerick.
Mr. Justice Robert Day (1746–1841), the Diaries and the Addresses to Grand Juries (2004);
The Pocket History of Kerry (2007);
The History of Tralee, Its Charter and Governance (2009);
The Earls of Desmond, The Rise and Fall of a Munster Lordship (2013)