Admiral Sir John Heffernan's parents, Daniel Harold Heffernan and Mary Dallimore, were married at St Mary Magdalene, Gillingham, Kent in 1831.

They had five children:

1. Mary Ann b 1838 Chatham d 1841
2. Eliza b 1836 Chatham; in 1851 a servant alongside parents
3. Ellen b 1832 Chatham
4. John Harold b 1834 Rochester, d 1921 Burton upon Trent
5. Richard b 1840 d 1841 Medway

Daniel Heffernan was born circa 1809 in Blarney, Cork, Ireland, possibly at Garrycloyne. He died 1873 in Portsea. According to the British Regimental Register, Canada, he enlisted 10th Nov. 1829 with the 1st Battalion 84th Cork Foot Soldiers. On his marriage in 1831 he is described as a private in the East India Company. Later entries in publications such as Debrett's describe him as D Heffernan MD, HEICS of Carisbrooke. This was an attempt by his son to distance himself from his humble origins. In 1841 Daniel [David Heffeman] was living at Brompton Barracks, Gillingham, Kent. In 1851 he [Hefferman] is a solider in the E I C living as a servant to a sergeant-major. In 1861 he is living with a family in Soho and in 1871 is described as a retired commercial clerk living in Carisbrooke, Isle of Wight. It is possible that Daniel's parents were John  Hefferman b 1771 Cork and Ellinor Barry b 1775.

Mary Dallimore family came from the Isle of Wight. Her parents Richard Dallimore (1779 - 1822) and Martha Linington married in Newport in 1802. He had been born in Calbourne. His father, Richard Dallimore (1739 Thorley - 1823 Calborne) had been a veterinary surgeon. He married Martha  Rogers, of Carisbrooke,  in 1768 at Arreton.

Richard's parents were Joseph Dallimore (1698 Northwood - 1757) and Kezia Gleed (1702 - 1757). Joseph was a yeoman farmer in Wippenham and also a tenant in Northwood. In 1757-8 Joseph, Kezia and their son all died from smallpox.

Joseph's parents Thomas Dallemore (1661-1729) and Martha 91660-1749) were farmers in the parish of Northwood. Thomas's parents, John Dallemory (1640-1679) and his wife Elizabeth Cooke (1632-1705) also farmed in Northwood. John's father was John Dallemory (1619-1702).