Hi there,
First of all, what religion were they? Did Catherine marry in St. Peter's parish or church? Have you already checked church/civil registration records for this marriage?
St. Peter's civil parish looks like it may be in one or two Catholic parishes. I think perhaps Haddington Road, Donnybrook, possibly Rathmines and Booterstown. It depends on which church. I can give you the details for all parishes.
There are Roman Catholic church records available for Donnybrook. These date from 1871 for baptismal records and 1877 for marriage records. You can find these at the National Library of Ireland, Pos. 9309.
Haddington Road. These date from 1849 for both baptismal and marriage records. You can find these at the National Library of Ireland, Pos. 9214. See also Pos. 9215 for miscellaneous indexes.
Rathmines. These date from 1823 for both baptismal and marriage records. You can find these at the National Library of Ireland, Pos. 9200 (bapt. to 1886, marr. to 1881 Pos. 9201).
Booterstown. These date from 1755 for both baptismal and marriage records. You can find these at the National Library of Ireland, Pos. 9084 (b); 9085 (m).
If you have any difficulty, you could try writing to the parish priest for more assistance.
You mentioned a census, which census are you talking about? Where did Catherine die? In Ireland or England?
You should check a few other documents for possible information:
Civil registration records are available from the General Register Office (GRO). These start from 1864 however. You can access the website here: http://www.groireland.ie/research.htm
You could also try checking the land records called the Tithe Applotment Books (1823-38) or the later Griffith's Valuation (1848-64). Griffith's is freely available here: www.askaboutireland.com or here: www.failteromhat.com Failte Romhat has lots of other useful links you could try looking at. Tithe Applotment Books (1823-38). Microfilm copies of the books for all of Ireland are available at the National Archives of Ireland (NAI) http://www.nationalarchives.ie/genealogy1/genealogy-records/tithe-applotment-books-and-the-primary-griffith-valuation/ or the Church of Latter Day Saints (LDS).
You should consult the Uk National Archives for anything connected to their lives in England: http://www.nationalarchives.gov.uk/
This might be of interest:
St. Peter's Parochial Male & Femaile Boarding Schools, Sunday, Daily & Infant Schools: Reports 1850-60, National Library of Ireland, p. 439.
Please make sure you link anyone else in your family who is interested in their Irish heritage to our site - and indeed anyone else you know of Irish heritage.
Kind regards,
Sinead Cooney
Genealogist (Ireland XO)