Thomas married Elizabeth Starkey, a young woman of humble origin, They lived happily together, and had three daughters: Susan, married in 1796 to the 3rd Earl of Guilford; Frances, married in 1800 to John, 1st Marquess of Bute; and Sophia, married in 1793 to Sir Francis Burdett.
Mrs Coutts died in 1815. Soon after her husband married the popular actress, Harriot Mellon, leaving to her the whole of his immense fortune. He died in London on 24 February 1822. In 1827, his widow married the 9th duke of St Albans. She died ten years later, bequeathing her property to Angela, youngest daughter of Sir Francis Burdett, who then assumed the additional name and arms of Coutts. In 1871, this lady was created Baroness Burdett-Coutts
Frances 'Fanny' Coutts (1773–1832), Second Wife of the 1st Marquess of Bute