Sir William Knighton, 1st Baronet, GCH (1776 – 11 October 1836) was Private Secretary to the Sovereign under George IV (1822–1830).

He spent two years at Guy's Hospital, London, and received a diploma from the University of St Andrews in 1797.

He was also auditor of the Duchy of Lancaster, and from 1821 to 1830 was unofficially private secretary to the king and formally Keeper of the Privy Purse.

In an almost unprecedented move, the king surrendered control of his financial affairs to Knighton in 1822, on account of his enormous debts.

He had an unparalleled influence over the king, and letters from him to Knighton were addressed "M[y] D[ear] F[riend]," unlike the normal third person that was associated with the sovereign.