On 29 August 1831, he married firstly Harriet Georgiana Cosby, youngest daughter of Thomas Cosby, of Stradbally Hall and his wife Charlotte Elizabeth Kelly (daughter of Rt. Hon. Thomas Kelly, Second Justice of the Common Pleas of Ireland).[6] Together, they were the parents of two daughters and three sons, including:[7]
Hon. Charlotte Elizabeth Trench (1832–1854), who died unmarried.[7]
Hon. Harriette Mary Trench (d. 1884), who married, as his first wife, Maj. Hon. Frederick Le Poer Trench (1835-1913), second son of the 3rd Earl of Clancarty, in 1883.[8] Frederick was the older brother of her brother's wife Lady Anne.[7]
Trench died, aged 75, at Clonodfoy (otherwise known as Castle Oliver) and was buried at the family's mausoleum at Woodlawn, County Galway, a week later.[10] His older son Frederick having predeceased him in 1879, he was succeeded in the barony by his grandson Frederick.[10] His second surviving son Cosby, who inherited Castle Oliver, was a soldier and magistrate.[10]