Dean Cogan was a nineteenth century Roman Catholic Irish priest (awarded the religious title of dean) who wrote a famous history of the Diocese of Meath in Ireland. Published in two volumes in 1862 and 1867, Cogan's The Diocese of Meath remains required reading for anyone interested in the history of christianity in Ireland. This is because Cogan had access to three sources of information no longer available to historians;
- folklore and memories of people alive in Meath the 1850s and 1860s (covering the period from the anti-catholic Penal Laws to the Irish Potato Famine (1845-49)) which were recorded by no other contemporary source in such detail;
- access to the Meath diocese's archives; when the Roman Catholic Bishop of Meath moved from his former seat in Navan to the new cathedral in Mullingar in the early twentieth century (the diocesan seminary, St. Finians, also moved from Navan to Mullingar) the diocesan archives were lost in the process. How the priceless records, many of them by Cogan in his research in the 1860s, were lost remains a mystery;
- access to papers relating to the church in Meath in the Irish Public Records Office. The Irish Public Records Office was deliberately blown up by the Anti-Treaty IRA in 1922, in the process destroying one thousand years of records, including including most of the records from that source quoted by Cogan.
Cogan's work led to the naming of a street, Dean Cogan Terrace in his memory in Navan, where he had served as a curate.