Clemens August, Freiherr von Westphalen zu Fürstenberg[a] (Reichsgraf[b] from 1792; 12 January 1753 – 26 December 1818) was a German aristocrat who held numerous offices in various North-West German Bishoprics and served as Minister of State of the Electorate of Mainz and Imperial Envoy.

He was a Wirklicher Geheimer Rat (equivalent to Active Privy Councillor in the Russian Empire) and Master of the Horse in Hildesheim and Paderborn.

He was also the Minister of State of the Electorate of Mainz and, as such, the second Ambassador in the 1790 imperial election following the death of Emperor Joseph II.

For many years he was Imperial Envoy with the rank of Minister Plenipotentiary at the Courts of the Electors of Cologne and Trier as well as at the Lower Rhenish–Westphalian Circle.

Westphalen took over the family estates in 1778 and was able to increase the family's wealth considerably, as he was the sole heir of the Prince-Bishops Wilhelm Anton von der Asseburg, his great-uncle on his mother's side, and Friedrich Wilhelm von Westphalen, his uncle on his father's side.

The estate had been owned by the Rhenish noble family Langwerth von Simmern (who had acquired it from the Knights of Allendorf of 1797).