Which Call of Duty game was the last developed by Infinity Ward before the 2010 studio split?

Call of Duty: Modern Warfare 2 was the last game developed by Infinity Ward before the studio split in 2010.

Released in November 2009, Modern Warfare 2 was Infinity Ward’s direct sequel to Call of Duty 4: Modern Warfare. It continued the story of Captain Price and Task Force 141 while introducing major characters such as Sergeant Gary “Roach” Sanderson and the antagonist Vladimir Makarov. The game also became one of the decade’s most commercially successful shooters.

The studio crisis followed several months later. On March 1, 2010, Infinity Ward co-founders Jason West and Vince Zampella were dismissed by Activision. Numerous employees subsequently left, with many joining the pair at their new studio, Respawn Entertainment.

Modern Warfare 3 was released in 2011 and involved Infinity Ward, but it was produced after the split and was co-developed with Sledgehammer Games and supported by other studios. That timing is why Modern Warfare 3 is not the answer. Call of Duty 4 came earlier, while Ghosts was released in 2013.