Hi Melaney, Having learnt the hard way about known used variants spellings being found later, I delayed my first reaction because one of your spellings O'Roidan was one I had not encountered, so I looked up the
http://www.irishtimes.com/ancestor for Reardon. It starts simply with those found in Griffiths primary valuation more later ie
O'Reardon 7. O'Riordan 21, Reardan 3, Rearden 2. Reardon 444, Reordan 3
Rierdon 5, Riordan 1107, Riordon 20. This is then followed by a much larger list of other spellings and their sources.
So I went back to the 1861 English Census, the entries are made by an enumerator which puts the spelling out of the family name at risk. the version I looked up has his occupation as Waiter rather than Writer but when I looked up the original I can read it as either. Their address as Lucas Street. Parish Rotherhithe Ecclesiastical District Christchurch London, Surrey. I noted Ellen eldest born Bermondsey.
{ Table 2: Boundary Changes affecting Bermondsey Registration Description of Change
Population transferred 1.1.1870 (abolished) (a)Lost the parish of Bermondsey to St. Olave Southwark registration district. 41659 in 1861. You have found them on other census I didn’t,
Some 40 years later there is a Patrick Riordan Birth Year 1833 Age 68 Birth Place Ireland Boarder Labourer In Iron Works Single living in Manor Road Erith County Kent Ecclesiastical District Christ Church Source 1901 English Census
So next I extracted the 21 Patrick Reardon named as householders in Co Cork in 1850-1855 in Ireland in Griffiths Valuation in Ireland.see
http://www.failteromhat.com/griffiths.php or
www.askabout ireland.com to see if any clues
Surname First Name civil Parish townland
Reardon Patrick Ardagh Breeda
Reardon Patrick Ardnageehy Glenville
Reardon Patrick Ballymodan Clancool Road,Cloghmacsimon
Reardon Patrick Ballymoney Ballynacarriga
Reardon Patrick Ballymoney Garranure
Reardon Patrick Ballymoney Kilcaskan
Reardon Patrick Caherlag Vill of New Glanmire,Lackenroe
Reardon Patrick Clonfert Knockilly
Reardon Patrick Clonmel Ballynacrusha
Reardon Patrick Fanlobbus Castle St,Dunmaway
Reardon Patrick Grenagh Glancam
Reardon Patrick Kilbrogan Gurteen
Reardon Patrick Lisgoold Lisgoold North
Reardon Patrick Little Island Courtstown
Reardon Patrick Magourney Madrid Coachford Village
Reardon Patrick St. Annes Shandon Goulding's Lane
Reardon Patrick St. Annes Shandon Old Youghal Road
Reardon Patrick St. Finbars Pickett's Lane
Reardon Patrick St. Marys Shandon Conway's Lane Cork
Reardon Patrick Templerobin East-Ferry Rd,Queenstown,(Carrignafoy)
Reardon Patrick Whitechurch Monard
If this could be reduced to one or two there is a chance but I think it is just too many. So although I set out to try to help you I didnt get anywhere. You have done well getting as far as trying to identify this MysteryMan
Hoping others can build you links
JimG