Eastmeath as a placename is little used nowadays except for elections when Co Meath becomes the onstituency of Eastmeath. The 1821 census for the area shows a James McCann (26) and his wife Catherine (25) and daughter Mary (2) living in the mill house at Rathnally where he is described as "Millers Clerk". The mill was owned by the Thompson family, the local landowners who lived in Rahnally House and the lessee at the time was John McCann who also had a wife named Catherine . John McCann lived nearby on a farm in Kilcooly where they had 10 children, one named John but none named Margaret. As far as I know James the miller's clerk and John the miller and farmer were not related. Lots of McCanns in Eastmeath. Best of luck but finding a place of brth is essential.