Despite spending much of his time in London, linked to his parliamentary and judicial duties, and the fact that Nicholl held all his political seats in
England, he continued to foster and support links with his home country of Wales. In 1787 he married Judy Birt, the youngest daughter of
Peter Birt of
Wenvoe Castle, and spent his time during his political career split between his London town house and Tondu House in South Wales. Nicholl and Judy had one son and three daughters. Nicholl's only son, also
John Nicholl, would later follow his father's political career, becoming a Member of Parliament for Cardiff.
Merthyr Mawr House Nicholl had amassed several estates throughout his lifetime, mainly through inheritance. He had gained an interest in property in Llantwit Major from his godfather, the Rev John Nicholl in 1770 and when Edward Powell died in 1771, he too left estates to Nicholl in five local parishes, including Tondu House. But despite these holdings, when Nicholl came to building his own family home, he chose the area of
Merthyr Mawr. When Charles Bowen died in 1797, Nicholl was a trustee appointed to effect the will. Bowen owned large estates within Merthyr Mawr, but they were heavily mortgaged and there were additional debts and legacies to be honoured. Nicholl took this opportunity to purchase of the estate, eventually agreed at £18,000. Nicholl initiated plans to construct a country house on the estate in 1806, demolishing the old residence, a 16th/17th century hall of the Stradling family, and hiring architect Henry Wood to build Merthyr Mawr House. Wood and Nicholl parted company in 1808, but Nicholl pushed through with his plans and moved into the incomplete building in 1809. When the mansion was completed it was notable for its library, which was reported as holding 30,000 articles. Maerthyr Mawr house is a five bay, two-storey classical mansion faced in white local
carboniferous limestone, with a
hipped roof and a sash windows, and central single-storey porch with Tuscan columns in the north front. The mansion and its outlying stables are presently classed as Grade II* listed buildings. ==References==