Franz Freiherr von Mercy (or Merci), lord of Mandre and Collenburg (died 1645), was a German general in the Thirty Years' War. He was born of a noble Lorraine family at Longwy some time between 1590 and 1598. From 1606 to 1630 he was engaged in the imperial service. By the latter year he had attained high military rank, and after distinguishing himself at the first Battle of Breitenfeld (1631) he commanded a regiment of foot on the Rhine and defended Rheinfelden against the Swedes with the utmost bravery, surrendering only after enduring a five-months' siege. Mercy spent the remainder of his life in military service. He was killed at the Battle of Nordlingen in 1645.