| Maddoxgarden | Garraí Mhadóg | Townland | | C | 1851 | L | 2003 |
| Maddoxland | Fearann Mhadóg | Townland | | C | 1851 | L | 2003 |
| Magdalene Street | | | Moneymore | GV | 1851 | | |
| Maghereagh | An Machaire Riabhach | Townland | | C | 1851 | L | 2003 |
| Main Street | | | Dunleer | GV | 1854 | | |
| Main Street | | | Reval | GV | 1854 | | |
| Main Street | | | Clogher | GV | 1854 | | |
| Maine | Maighean an Bhradáin | Townland | | C | 1851 | L | 2003 |
| Mall, The | | | Yellowbatter (Drogheda Town) | T | 1886 | | |
| Manistown | Baile an Mhannaigh | Townland | | C | 1851 | L | 2003 |
| Manistown | | | Manistown | TAB(A) | 1830? | | |
| Mansfieldstown | Baile Mhic Mháirtín | Townland | | C | 1851 | L | 2003 |
| Mansfieldstown | Baile Mhic Mháirtín | Civil Parish | | C | 1851 | L | 2003 |
| Mapastown | Baile an Mhápasaigh | Townland | | C | 1851 | L | 2003 |
| Mapastown | Baile an Mhápasaigh | Civil Parish | | C | 1851 | L | 2003 |
| Maplestown | | | Mapastown | FWS | 1908 | | |
| Mapperstown | | | Mapastown | FWS | 1908 | | |
| Market Square | | | Collon | GV | 1854 | | |
| Market Square | | | Townparks (Dundalk) | GV | 1854 | | |
| Market Square | | | Liberties of Carlingford | GV | 1854 | | |
| Market Street | | | Townparks (Ardee) | GV | 1854 | | |
| Market Street | | | Townparks (Dundalk) | GV | 1854 | | |
| Marlay | Baile Bhearlaí | Townland | | C | 1851 | L | 2003 |
| Marlestown | Baile Bhearlaí | Civil Parish | | C | 1851 | L | 2003 |
| Marsh, North | An Méirse Thuaidh | Townland | | C | 1851 | L | 2003 |
| Marsh, South | An Méirse Theas | Townland | | C | 1851 | L | 2003 |
| Marsh, The | | | Lagavooren (Drogheda Town) | T | 1886 | | |
| Marshallrath | Ráth an Mharascalaigh | Townland | | C | 1851 | L | 2003 |
| Marshes, Lower | Na Méirsí Íochtaracha | Townland | | C | 1851 | L | 2003 |
| Marshes, Upper | Na Méirsí Uachtaracha | Townland | | C | 1851 | L | 2003 |
| Martin's Fort | | | Edmondstown | FWS | 1908 | | |
| Martinstown | Baile an Mháirtínigh | Townland | | C | 1851 | L | 2003 |
| Mary Street | | | Lagavooren (Drogheda Town) | T | 1886 | | |
| Maudelins, The | | | Rath (Ballybarrack Civil Parish) | FWS | 1908 | | |
| Maynbroddask | | | Maine (?) | FWS | 1908 | | |
| Mayne | An Mhaighean | Townland | | C | 1851 | L | 2003 |
| Mayne | An Mhaighean | Civil Parish | | C | 1851 | L | 2003 |
| Mayorality Street | | | Yellowbatter (Drogheda Town) | T | 1886 | | |
| Mayoralty Street | | | Moneymore | GV | 1851 | | |
| McArdle Court | | | Townparks (Dundalk) | GV | 1854 | | |
| McGovern's Court | | | Moneymore (Drogheda town) | T | 1886 | | |
| McKenna's Lane | | | Mell | GV | 1854 | | |
| McKenna's Lane | | | Mell | GV | 1851 | | |
| McKenna's Lane | | | Moneymore (Drogheda town) | T | 1886 | | |
| Meaghsland | Fearann na Míoch | Townland | | C | 1851 | L | 2003 |
| Meeting Street | | | Liberties of Carlingford | GV | 1854 | | |
| Meganstown | | | Wyanstown | FWS | 1908 | | |
| Mell | Meille | Townland | | C | 1851 | L | 2003 |
| Mell Lane | | | Mell | GV | 1854 | | |
| Mellifont | An Mhainistir Mhór | Townland | | C | 1851 | L | 2003 |
| Mellifont Park or Louth Hill | Páirc na Mainistreach | Townland | | C | 1851 | L | 2003 |
| Meolston | | | Thomastown (?) | FWS | 1908 | | |
| Merchants' Quay | | | Yellowbatter (Drogheda Town) | T | 1886 | | |
| Milestown | Baile Mhílis | Townland | | C | 1851 | L | 2003 |
| Mill Lane | | | Liberties of Carlingford | GV | 1854 | | |
| Mill Lane | | | Moneymore (Drogheda town) | T | 1886 | | |
| Mill Street | | | Townparks (Dundalk) | GV | 1854 | | |
| Millars' Field | | | Castlebellingham | M(n) | 1930 | | |
| Millfield Fort | | | Stabannan | FWS | 1908 | | |
| Millgrange | Gráinseach an Mhuilinn | Townland | | C | 1851 | L | 2003 |
| Millockstown | Baile Mhiológ | Townland | | C | 1851 | L | 2003 |
| Millpark | Páirc an Mhuilinn | Townland | | C | 1851 | | |
| Milltown (Civil Parish of Barronstown) | Cnoc an Mhuilinn | Townland | | C | 1851 | L | 2003 |
| Milltown (Civil Parish of Dysart) | Baile na Muileann | Townland | | C | 1851 | L | 2003 |
| Milltown (Civil Parish of Termonfeckin) | Baile an Mhuilinn | Townland | | C | 1851 | L | 2003 |
| Milltown (Civil Parish of Dromiskin) | Baile an Mhuilinn | Townland | | C | 1851 | L | 2003 |
| Milltown Bog | Currach Chnoc an Mhuilinn | Townland | | C | 1851 | L | 2003 |
| Milltown, Grange | Gráinseach Bhaile na Muileann | Townland | | C | 1851 | L | 2003 |
| Milltown, Old | Seanbhaile na Muileann | Townland | | C | 1851 | L | 2003 |
| Miselrath | | | Louth Hall (?) | FWS | 1908 | | |
| Mitchelstown | Baile Mhistéala | Townland | | C | 1851 | L | 2003 |
| Moatefield | | | Priestown | FWS | 1908 | | |
| Mollagha Loght | | | Tinure and Rathdaniel | FWS | 1908 | | |
| Monascreebe | Móin na Scríbe | Townland | | C | 1851 | L | 2003 |
| Monasterboice | Mainistir Bhuithe | Townland | | C | 1851 | L | 2003 |
| Monasterboice | Mainistir Bhuithe | Civil Parish | | C | 1851 | L | 2003 |
| Monavallet | Muine Bhálait | Townland | | C | 1851 | L | 2003 |
| Moneshevin | | | Kilcroney and Darver | FWS | 1908 | | |
| Money Gole | | | Slievenaglogh | FWS | 1908 | | |
| Moneyboy | | | Bellurgan | FWS | 1908 | | |
| Moneycrockroe | Móin na gCnoc Rua | Townland | | C | 1851 | L | 2003 |
| Moneymore | An Mhónaidh Mhór | Townland | | C | 1851 | L | 2003 |
| Moneymore | | | Carlingford | FWS | 1908 | | |
| Moneyveg | | | Windmill | FWS | 1908 | | |
| Monksland | Fearann na Manach | Townland | | C | 1851 | L | 2003 |
| Monksrebaghe | | | Monascreebe | FWS | 1908 | | |
| Montana al'Knock | | | Knockaleva | FWS | 1908 | | |
| Moor Hall | | | Townparks (Ardee) | GV | 1854 | | |
| Mooremount (Civil Parish of Cappoge) | Baile Ardach | Townland | | C | 1851 | L | 2003 |
| Mooremount (Civil Parish of Dromin) | Baile Ardach | Townland | | C | 1851 | L | 2003 |
| Moore's Court | | | Yellowbatter (Drogheda Town) | T | 1886 | | |
| Moore's Lane | | | Moneymore | GV | 1851 | | |
| Moore's Lane | | | Moneymore (Drogheda town) | T | 1886 | | |
| Mooretown | An Lorgain | Townland | | C | 1851 | L | 2003 |
| Moorland | An Currach | Townland | | C | 1851 | L | 2003 |
| Moretown | | | Rogerstown | FWS | 1908 | | |
| Morganstown | Baile na Muireagánach | Townland | | C | 1851 | L | 2003 |
| Mosstown | Baile Mhuiris | Civil Parish | | C | 1851 | L | 2003 |
| Mosstown, North | Baile Mhuiris Thuaidh | Townland | | C | 1851 | L | 2003 |
| Mosstown, South | Baile Mhuiris Theas | Townland | | C | 1851 | L | 2003 |
| Mount Oriel | | | Collon | FWS | 1908 | | |
| Mount Pleasant | | | Coolfed and Aghaboys | FWS | 1908 | | |
| Mountain-town | Sliabh Dhún Léire | Townland | | C | 1851 | L | 2003 |
| Mountbagnall | Moin Bhagnail | Townland | | C | 1851 | L | 2003 |
| Mountdoyle | An Carraigín | Townland | | C | 1851 | L | 2003 |
| Mounthamilton | Móta an Hamaltúnaigh | Townland | | C | 1851 | L | 2003 |
| Mountrush | Muine Rois | Townland | | C | 1851 | L | 2003 |
| Moyendales | | | Mayne and Dales | FWS | 1908 | | |
| Moyllenston | | | Mullanstown (?) | FWS | 1908 | | |
| Much Aishe | | | Ash, Big | FWS | 1908 | | |
| Muchgrange | An Ghráinseach Mhór | Townland | | C | 1851 | L | 2003 |
| Mucklagh | An Muclach | Townland | | C | 1851 | L | 2003 |
| Muff | An Magh | Townland | | C | 1851 | L | 2003 |
| Mullabane (Civil Parish of Carlingford) | An Mullach Bán | Townland | | C | 1851 | L | 2003 |
| Mullabane (Civil Parish of Clonkeen) | An Mullach Bán | Townland | | C | 1851 | L | 2003 |
| Mullabohy | Mullach na Boithe | Townland | | C | 1851 | L | 2003 |
| Mullacapple | Mullach an Chapaill | Townland | | C | 1851 | L | 2003 |
| Mullacloe | Mullach Cló | Townland | | C | 1851 | L | 2003 |
| Mullacrew | Mullach Craoibhe | Townland | | C | 1851 | L | 2003 |
| Mullacurry | Mullach Curraigh | Townland | | C | 1851 | L | 2003 |
| Mulladrilan | | | Charlestown | FWS | 1908 | | |
| Mulladrillen | Mullach Drislinn | Townland | | C | 1851 | L | 2003 |
| Mulladrillen | | | Mulladrillen | TAB(A) | 1830? | | |
| Mullagh an Capall | | | Newtowndarver | FWS | 1908 | | |
| Mullagh Bwee | | | Castletowncooley | FWS | 1908 | | |
| Mullagh Disseline | | | Mullaghdrillen | FWS | 1908 | | |
| Mullagh Disserne | | | Mullaghdrillen | FWS | 1908 | | |
| Mullagh Luin | | | Dromiskin | FWS | 1908 | | |
| Mullagh Ullagh | | | Bawn | FWS | 1908 | | |
| Mullagh Usker | | | Summerhill | FWS | 1908 | | |
| Mullagharlin | Mullaigh Chairlinn | Townland | | C | 1851 | L | 2003 |
| Mullagharnagh | | | Salterstown | FWS | 1908 | | |
| Mullaghash | | | Belpatrick and Funshog | FWS | 1908 | | |
| Mullaghattin (Civil Parish of Ballymascanlan) | Mullach Aitinne | Townland | | C | 1851 | L | 2003 |
| Mullaghattin (Civil Parish of Carlingford) | Mullach Aitinne | Townland | | C | 1851 | L | 2003 |
| Mullaghdoo | | | Collon | FWS | 1908 | | |
| Mullagherin | | | Milltown (Dromiskin Civil parish) | FWS | 1908 | | |
| Mullaghmore | | | Loughanmore (Mansfieldstown Civil Parish) | FWS | 1908 | | |
| Mullaghmore | | | Corbollis | FWS | 1908 | | |
| Mullaghroe | | | Collon | FWS | 1908 | | |
| Mullameelan | Mullach Maoláin | Townland | | C | 1851 | L | 2003 |
| Mullameelin | | | Mullameelan | TAB(A) | 1830? | | |
| Mullamore | An Mullach Mór | Townland | | C | 1851 | L | 2003 |
| Mullanstown | Baile Mhoilin | Townland | | C | 1851 | L | 2003 |
| Mullary | Mol Áirí | Civil Parish | | C | 1851 | L | 2003 |
| Mullatee | Mullach an tSí | Townland | | C | 1851 | L | 2003 |
| Mullavally | Mullach an Bhaile | Townland | | C | 1851 | L | 2003 |
| Mullincross | Muileann Cros | Townland | | C | 1851 | L | 2003 |
| Mullin's Fort | | | Whiteriver | FWS | 1908 | | |
| Mullinstown | | | Mullanstown | TAB(A) | 1930? | | |
| Murray's Fort | | | Tullakeel | FWS | 1908 | | |
