Hi CC,
I will see can I assist you. Irene has given you a good guide as to where to search.
First of all I searched Roots Ireland (subscriptions site) for the births of John and Robert Shannon without success. I found a marriage for Thomas Shannon but the wife is unknown, if this is it, it may fit with the birth of John & Robert.
01-Aug-1835
Parish / District: KILLESHANDRA County: Co. Cavan
Husband Wife
Name: Thomas Shanon Unknown
Address:
Denomination: Roman Catholic Roman Catholic
Occupation:
Age:
Status:
Husband's Father Wife's Father
Name:
Address:
Denomination:
Occupation:
Husband's Mother Wife's Mother
Name:
Address:
Denomination:
Occupation:
Witness 1 Witness 2
Name: Thomas Shanon Anne Fitzpatrick
Address:
Notes:
DATE IN AUGUST APPROXIMATE.
© 2020 Copyright Cavan Genealogy
I then started to look for the death of Thomas Shannon, hoping that he survived after civil registration began in 1864. These records are free to search on irishgenealogy.ie
I found a Thomas Shannon who died in 1926 at the grand age of 95 in the townland of Gortnavreeghan in the district of Bawnboy, Thomas was still married, which means his wife was alive and his son Robert was in attendance. There are two other deaths in 1865 & 1876, but their images are not available yet. There are a couple in the district of Cavan that also could be his father.
I searched for births for Mary Blake on RootsIreland and I found two, but they are possibly too late:
Mary Blake Date of Birth:
Date of Baptism: 20-Aug-1832
Address: Knocknagarton Parish/District: CASTLERAHAN
Gender: Female County Co. Cavan
Denomination: Roman Catholic
Father: Thomas Blake Mother: Rose Doonegan
Occupation:
Sponsor 1 /
Informant 1: Thomas Magauran
Sponsor 2 /
Informant 2: Bridget Doonegan
Mary Blake Date of Birth:
Date of Baptism: 08-Dec-1833
Address: Parish/District: LOCH GOWNA
Gender: Female County Co. Cavan
Denomination: Roman Catholic
Father: Edward Blake Mother: Anne Keogan
Occupation:
Sponsor 1 /
Informant 1: Patt Tuite
Sponsor 2 /
Informant 2: Catherine Cullin
I also searched for her death on irishgenealogy.ie and again there are some images not available, but you can purchase them and see if you can make any connections with the other records.
In searching the records the surname Shannon appears to be mainly in the west of the county, but there are always anomalies. You could also contact Cavan Genealogy as follows, they will do research for a fee.
Cavan Genealogy
1st Floor, Johnston Central Library, Farnham St., Cavan
Tel: +353 (0) 49 4361094
Email: cavangenealogy@eircom.net
I hope I have given you some other paths to focus your search on, if you wish to check anything with me please do.
Regards Carmel O'Callaghan