try ulster architectural history society
some devitt marriages  all too late but no births or burials from 
https://www.ancestryireland.com/DEVITT   JAMES   1850   father BERNARD   Armagh   
DEVITT   JAMES   1851      Down   
DEVITT   JAMES   1851      Down   
DEVITT   JAMES   1851   father WILLIAM   Antrim   
DEVITT   JAMES   1869      Down
no trace in Belfast street directories up to 1819 
http://www.lennonwylie.co.uka will did exist for a James in Cullin.  Cullin townlands existed in Cavan, Fermanagh, Meath. see 
https://apps.proni.gov.uk/ProniNames_which suggests Co Fermanagh. 
 by ear rather than spelling Deveight House   Blaris   .   in Lisburn; death of Dr Emerson Wilson Henry , brother of W. Tennent Henry 10 Dec 1881   DR
then I found in Ros Davies Co Down website  this is her message board 
http://freepages.genealogy.rootsweb.ancestry.com/~rosdavies/WORDS/RollCall.htm#DJames   DEVITT   ?   of Devitt Hall, Co. Down; father of Rev. Clotworthy Devitt Esq. of the General Post Office , Dublin, married Jane Buck the only daughter of Andrew Buck 
Esq. eminent Attorney of this City(Dublin)   terry.murfitt ' at ' virginmedia.com
Genes Reunited has birth index for tree holders entries, you join to contact tree holders
James   Devitt   1810   Unk ...   No   Elizabeth   Find out more
James   Devitt   1800   Ireland ...   No   Anthony   Find out more
James   Devitt   1799   Ireland ...   No   Andrew   Find out more
James   Devitt   1795   Ireland ...   No   Steve   Find out more
James   Devitt   1790   Ireland ...   No   Victoria   Find out more
James   Devitt   1788   Doolan, Clare, Irela...   No   Arthur   Find out more
James   Devitt   1788   Co Clare, Ireland ...   No   Paul   Find out more
James   Devitt   1760   Ireland ? ...   No   Paul Find out more
I didnt give up and tried again searching for Devitt in Ulster 1790 +or- 50 years
William   Devitt   1820   Belfast County Antri...   No   David   Find out more
Clotworthy   Devitt   1787   Antrim County Antrim...   No   Paul Find out more
 I need to stop now
keep going