Helen:
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Roots Ireland (subscription site) has the baptismal record for Robert and three older siblings (see below). Also, found the 1830 marriage record for the parents. There may have been other children between 1830 and 1837. The 1855 Griffiths Valuation head of household listing for Annagelliff civil parish shows William Darby in Latt townland as you indicated.
I was not able to locate a civil or church marriage record for Robert and Mary Anna Miller.
Roger McDonnell
Name:Robert DarbyDate of Birth:
Date of Baptism:01-Apr-1849Address:
Parish/District:CAVANGender:MaleCountyCo. Cavan
Denomination:Roman Catholic
Father:William DarbyMother:Eleanor GillholyOccupation:
Sponsor 1 /
Informant 1:Michael Gillhooly Sponsor 2 /
Informant 2:Anne Tierny
Name:James DarbyDate of Birth:
Date of Baptism:23-Jun-1844Address:
Parish/District:CAVANGender:MaleCountyCo. Cavan
Denomination:Roman Catholic
Father:William DarbyMother:Ellen GilloolyOccupation:
Sponsor 1 /
Informant 1:Patrick Sheridan Sponsor 2 /
Informant 2:Anne Ronan
Name:Joan DarbyDate of Birth:
Date of Baptism:14-Mar-1841Address:
Parish/District:CAVANGender:FemaleCountyCo. Cavan
Denomination:Roman Catholic
Father:William DarbyMother:Ellen GilulyOccupation:
Sponsor 1 /
Informant 1:Patrick Olwill Sponsor 2 /
Informant 2:Bertha Teirney
Name:Eleanor DarbyDate of Birth:
Date of Baptism:07-May-1837Address:
Parish/District:CAVANGender:FemaleCountyCo. Cavan
Denomination:Roman Catholic
Father:William DarbyMother:Eleanor GilowlyOccupation:
Sponsor 1 /
Informant 1:Thomas Tierney Sponsor 2 /
Informant 2:Eleanor Darby
Date of Marriage:27-May-1830
Parish / District:CAVAN
County:Co. Cavan
Husband WilliamDarby
Wife EleanorGilluly
Denomination:Roman Catholic
Roman CatholicOccupation: