Number 9 Mansfield Street is on the west side of the street, at the centre of the terrace, and was built for William Cobbett (ND). Cobbett is unknown, but he was doubtless one of the builders working on Mansfield Street as he was also involved in the Portland Place speculation, where he took the lease of number 25.
In 1773 the lease was purchased by Barbara Herbert, Dowager Countess of Powis (1735-86), the daughter of William Herbert, 2nd Marquess of Powis, and widow of Henry Herbert, 1st Earl of Powis, who had died one year earlier. The Countess retained the house until 1778.
Number 9 is one of the surviving houses, and Adam's drawing room ceilings remain in situ. It is now used as offices.