Murphy 
  Denis Murphy or Thomas Murphy?   
Elizabeth Blennerhassett married a Mr. Murphy.  
What is his first name?
- 
The copy of her half-brother's 1798 marriage settlement  
says she married "Denis Murphy".
- 
The baptism of her son Arthur in 1799 says his father is "Thomas Murphy" of Cromane, Killorglin parish.
- 
The 
[Tithe Survey, 1823-37]
shows only one Murphy in Cromane,   namely 
 "Dennis Murphy".
 
-  The Tithe Survey shows   two other Denis   Murphys  elsewhere  in   Killorglin  parish.
There is  no Thomas Murphy in   Killorglin  parish.
There is a T. Murphy in
 Knockaunroe, 
 Killorglin  parish.
Conclusion: I think, odd though it seems,  the baptism entry must be  a mistake and she married Denis Murphy.
 
  
Denis Murphy.
He mar pre-1798 to
 
 Elizabeth  Blennerhassett
[natural dau of  
Arthur Blennerhassett,   
descendant of 
Edward III].
She was Protestant (named as such on child's baptism).
He was Catholic (child baptised Catholic). 
The   copy of her half-brother Robert Blennerhassett's 
  
 1798  marriage settlement  
 in  
[NLI] D.27079 
refers to Elizabeth   as
"now [in 1798]  the wife of Denis Murphy".
  
They lived at 
Cromane, Killorglin par (W of Killorglin,
see 
map).
Pronounced "Cromawn".
Living Cromane as at son Arthur's bapt 1799.
Arthur's baptism 1799 calls the father  
"Thomas Murphy".
I think (see above) this is a mistake
and he must be Denis Murphy. 
"Dennis Murphy" is listed at Cromane  
in
[Tithe Survey, 1823-37].
He has a very poor holding of 3 acres of low quality land. 
There is a 
"Denis Murphy"     at Cromane Upper  in
  
[Griffiths Valuation, 1853].
This could be old Denis or a son.
Denis and Elizabeth  had issue:
-  Arthur Murphy,
 bapt  6 September 1799 [Killorglin RC par records].
 The   unusual name "Arthur"  is  clearly after his grandfather
Arthur Blennerhassett.
 The bapt was sp by  
"Lucy Hassett".
 
  
 
Baptism of Arthur Murphy, 6 September 1799, Killorglin RC par records.
"6th   [Fr. James Loony] baptised Arthur the son of Thomas Murphy and Elizabeth Hassett, Protestant.
Sponsor [illegible] and Lucy Hassett.
Cromane."
See 
larger
and 
full page.
From Killorglin RC church. Used with permission. 
 
"Dennis Murphy" listed at Cromane  
in
[Tithe Survey, 1823-37].
Location is "Cromane or Mountain part"
which would be Cromane Upper.
Land is 
"Reclaimed bog" 1 acre, 
 and "Commonage" 2 acres. 
He clearly has a very poor holding.
There are no other Murphys in Cromane.
From here.
 
 
 
Entries for 
"Denis Murphy"     at Cromane Upper  in
  [Griffiths Valuation, 1853], 
p.163 and p.164.
This could be old Denis or a son.
There are other Murphys in Cromane Upper. They may be related.
From here.