Mark Lannon appears on RC parish registers for Croghan and Elphin in the early 19th century. 

In 1814, Mark Lannon and Celia Gray of Lisnabol (north-west of Elphin) baptise their daughter Mary. They invited John Bolan and Brigid Mullaney to godparent. 

• John Bolan was living in Cloonmahaan/ Corracreigh (just south of Elphin near Cloonyquin). He was the brother of Peter Bolan and Edmund Bolan of Carrownurlar.
• Brigid Mullaney was living in Elphin and married to Patrick Conner. In 1810, they invited Sabina Branon (sic) to godparent.

Mark Lannen is then invited to godparent by his sister Sabina Lannon and Patrick Barrett of Ballinvilla. 

• Hugh O'Donnell aka McDonnell & Eleanor O'Hara (Croghan RC) invited Sabina Lannen to godparent in 1828; Margaret & Edmund Barrett in 1834; John Finn in 1837; Patrick Boyd & Anne Barrett in 1838, James McDonnell & Catherine Morahan in 1840. 

Mark Lannen does not appear in the Tithe Applotment Records of 1824 at Lisnabul nor anywhere else in Co Roscommon.  

Ó LEANNÁIN (sometimes pronounced Ó Lionnáin, or Ó Liondáin)

Anglicized: O'Lennane, O'Lennan, Linnane, Lannan, Lannen, Lannon, Lannin, Lennon, Lennan, Lennin Leonard; (In error: Laan? Laane? Lane? Lenaghan?)

'descendant of Leannán' (diminutive of leann, a cloak or mantle); the name of at least three distinct families, seated respectively in the counties of Fermanagh (Lisgoole near Enniskillen), Mayo (Killala) and Galway. All are still well represented, but very often disguised under the anglicised form of Leonard.

In Co. Roscommon, the most common spelling variant in the 18th century was Lannon followed by Lannin and Lannan. May be disguised by Lennon in the 20th cnetury. 

Elphin Census 1749

par. Killummod

Killummod TL: Cottagers Matthew & Mary Lennon RC (see bottom of page 67 for TL and profession) 3u.14 & 1 servant

par. CREEVE

Correnamady: cottier E M Lenon RC 1u.14

par. ELPHIN

Raheens: servant Charles Lennon widower RC 2 children over 14

Cloonvillane: Blacksmith Richard Linan & wife & 3 u.14

Clogher Beg: William Leanane & wife RC Servant nochildren | Patt Leanane & wife 2 under 14

par. ARDCARN

Luarton: labourers Simon Lenahan & wife RC | Will Lenahan & wife

par. BUMLIN near Strokestown

Butcher Con & Ellen Lannon (2 o. 14)

Scramoge: Farmer Hugh &  Ellen Lanon (2 serb¥vants)  | Tenant James & Ellen Lanon 2u.14 (2 servants) | labourer John & Mary Lanon (3 u.14) | Blacksmith Con & Mary Lanon |

Mulliveheran: Beggars Peter & Mable Lanon  

par. KILGLASS

Bartel Lannon and James Lannon appear in the same townland of  both with 2 children under the age of 14. 

par. ROSCOMMON

TL Roscommon labourer Daniel Lennon RC & wife & 3 u.14

Ballynagard: Villagers Val Lennan (2 u14 & Ed Lennan (1u14)

Gallowstown: Villager Dennis Lennan RC – had 4 servants (3male).

par KILNAMANAGH

Ballinvoher: Cottier Richard & Honor Lennon RC 3 u14

par CLOONFINLOUGH

Tumeever: labourer Luke Lenahon

The Flax Grower's list 1796:

Thomas Lannon par. Shankill

James Lannon Sr. par. Shankill

James Lannon Jr. par. Shankill

John Lannon par. Lissonuffy

Loughlin Lannon par. Kilglass

Bartholomew Lannon par. Kilglass

Edmund Lannon par. Kilmore

Connor Lannon par. Kilmore

Bryan Lannon par. Termonbarry

Michael Lennon par. Fuerty

Patrick Lane par. Killummod

1829 Edward Lennon & W Curneen, christen Edward Jr. in CROGHAN RC Godparents Andrew & Brigid Rock. 

1829 James Lannon of Ballinafad, Cloonfinough left a will. 

1829 Patrick Lannon of Culeen, Elphin, deceased, left a will. 

By 1857 (GV) the largest cluster was near Strokestown par. Cloonfinlough, Lissonuffy, Kilgefin, Termonbarry.

Also 1-2 families in the vicinity of Derryfeacle par. Kilglass, Clooncraff | Elphin par. Creeve | Carrick-on Shannon par Kiltoghert | Castlerea par. Kilkeevin