| Census of First Monaghan Presbyterian Congregation, 1821 | McMahon, TheoO'Neill, Marie | Article in Journal | | 2006 |
| Diamond memorials and vernacular monuments | McMahon, Theo | Article in Journal | | 2003 |
| Early memorials in Clones round tower graveyard and St. Tierney's R. C. graveyard, Roslea | McMahon, TheoMulligan, Patrick | Article in Journal | | 1984 |
| From Fintona to Wollongong, 1838 | McMahon, Theo | Article in Journal | | 1988 |
| Gravestone inscriptions in Drumswords cemetery, county Monaghan | McMahon, TheoMulligan, Patrick | Article in Journal | | 1985 |
| Inscriptions from St Tighernach's Church of Ireland graveyard, Clones | McMahon, TheoO'Neill, MarieSlowey, Sean | Article in Journal | | 1988 |
| Memorials in old Errigal cemetery, county Monaghan | McEntee, PatrickMcMahon, TheoMulligan, Patrick | Article in Journal | | 1988 |
| Rentals and reports of the Kane estate, Errigal Truagh, Co. Monaghan, 1764-1821 | McMahon, TheoO'Neill, Brendan | Article in Journal | | 1990 |
| Some additional gravestone inscriptions in Kilmore cemetery, county Monaghan | McMahon, TheoMulligan, PatrickO'Neill, Brendan | Article in Journal | | 1985 |
| Some county Monaghan abstracts from the1821 census | McMahon, Theo | Article in Journal | | 1991 |
| The Cottiers of the Shirley Estate in the civil parishes of Donaghmoyne, Killanny, Magheracloone and Magheross 1840-1847 | McMahon, TheoO Neill, Maire | Article in Journal | | 2010 |
| The Ker estate, Newbliss, Co. Monaghan, 1790-c. 1830 | McMahon, TheoO'Neill, Brendan | Article in Journal | | 1985 |
| The Rose estate, Tydavnet, county Monaghan | McMahon, Theo | Article in Journal | | 2004 |
| The tragic deaths in 1871 in county Monaghan of Emily and Mary Wilde - half-sisters of Oscar Wilde | McMahon, Theo | Article in Journal | | 2003 |
| Tully : the first fifty years : the story of a Monaghan town community | McMahon, Theo | Monograph or Collective Volume | Tully Residents' Association | 2007 |