- Born: ca. 1790, Ireland
- Marriage (1): Ellen Unknown
They possibly had a daughter named Brigid as there was one in the 1851 Census living in Tramore, Waterford, daughter of Denis & Ellen...
In the 1901 Census there is a Johanna Sullivan, Servant, 60, unmarried, born in Waterford, living on Main Street, recorded as House 29. Denis' son Thomas Denis named one of his daughters Johanna. She is just of an age to possibly be a daughter of Denis and a sister to Thomas Denis.
There is also a Mary Sullivan, Servant, 30, born in County Cork, living on Main St in a different house. And another Mary, widow, 42, a general Servant born County Waterford living in Post Office Lane. And husband and wife John & Mary Sullivan, 28 & 27, he a Farm Servant, she a Domestic Servant both born County Waterford, living in Summerhill, Tramore.
Denis married Ellen Unknown. (Ellen Unknown was born circa 1790 in Ireland and died before 1842 in prob, Ireland.)