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I "think" my great-great grandmother (Ellen Ledwith) was the daughter of Patrick Ledwith of Cylgeen and Bridget Keenan (?).....
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I see this couple as parents to several children in Co. Longford, so preume that's why they are on your list of 'possibles'.
Problem is, there are other Ledwith families with a father of the correct name that might be nearer to the location of your Ledwiths in Co. Westmeath.
The first couple are Patrick Ledwith & Margaret O'Neill in Ballynacarrigy district, Co. Westmeath, also a Patrick Ledwith and wife Catherine Conlon in Glassan district Co. Westmeath... It's also worth noting that these extracted records on FamilySearch are not complete, so there could be other births in Westmeath with a Patrick Ledwith as the father not listed in these.
Your Ellen was born very close to the start of civil records, so it's possible that she was not registered - or was born just before they started, in which case you would need to check for church records for a baptism.
Shane