The largest embassy in the world is the U.S. Embassy in Baghdad, Iraq. It is a sprawling complex located within Baghdad's fortified Green Zone. The embassy is exceptionally large, covering an area of 104 acres, according to the U.S. Department of State. It is significantly larger than other U.S. diplomatic missions abroad.
At 104 acres (42 ha), it is the largest U.S. diplomatic mission compound; nearly equal in area size to the Vatican City.[1]
https://en.wikipedia.org/wiki/Embassy_of_the_United_States,_Baghdad
https://en.wikipedia.org/wiki/Embassy_of_the_United_States,_Baghdad