David was born in 1806 in Llandilo Graban, Radnorshire, where his family had lived for several generations. He was the middle child in a family of 15 siblings. The family were farmers, and David followed his father's occupation. In 1841 he was farming at Penwern farm in Llandilo, with his widowed father and a couple of brothers living with him - David is listed first on the census, implying that he is the farmer, and the others are working for him.
Mary Williams was born in 1821 in Llanbedr Painscastle, the parish adjacent to Llandilo Graban. She was the illegitimate daughter of Elizabeth Williams. A year or so after Mary's birth, Elizabeth married Thomas Jones, and Mary took his surname. In 1841 Mary was living with her step-father, mother and younger siblings at Lower Pengarth farm in Llanbedr. Lower Pengarth is only half a mile from Penwern, so it's likely that the couple knew each other by this time.
In 1851, 43 year old David Pugh was farming at Pengarth in Llanbedr (the census doesn't say if this is Upper or Lower Pengarth). Visiting Pengarth is a 4 year old Alfred Jones born in Llandeilo. Meanwhile, Mary was visiting a nearby farm, Cwmyrhenllyn, with her sister.
The couple married in 1856 and continued farming. They had two children together, Henry born in 1858 and Mary Ann born in 1860. By Mary Ann's birth they were living in Aberedw, close to Llandilo Graban. On the 1861 census, the family were living at Pengarreg farm, Aberedw, Radnorshire, and consisted of David and Mary together with three children:
Alfred Pugh, son, aged 19
James Pugh, son, aged 9
Mary Ann Pugh, daughter, aged 1
I think that Alfred is the same Alfred who was living with David in 1851. I haven't been able to find Henry anywhere in 1861.
At some point in the 1860s, the family moved north to Llanbadarnfynydd, Radnorshire, where David began to farm Tynddol farm. On the 1871 census, David and Mary were there with James, Henry and Mary Ann.
David died on 25 July 1877 at Tynddol farm. His body was taken to Llandilo Graban to be buried with his parents. In his will he left the farm business to his two sons James David Pugh and Henry Pugh, with the wish that they would farm it together. Alfred was left 19 guineas. This suggests that Alfred was Mary's child but not David's, while James was David's son and possibly also Mary's.
Mary lived at Tynddol until her death on 23 September 1901. Tynddol was farmed by their son Henry until his death in 1908, when it passed on to his children.
There's still a lot I don't know about this family, particularly about the sons.