The Southern Island is the unnamed southern island of the Rook Islands. The second half of the story takes place on this island.
The island is "owned" by Hoyt Volker, who runs his slave trafficking business from the island, which is protected by hordes of bloodthirsty mercenaries known as the Privateers, and these mercenaries have superior equipment to that of the pirates and are organized like a military force.
Willis Huntley brings Jason Brody to the Southern Island with his plane. Jason goes undercover as a Privateer, under the alias of Foster, to rescue his younger brother Riley. He gets help from agent Sam Becker. Jason manages to kill Hoyt and rescue his brother, and together they fly back to the North Island using a Helicopter.
The Southern Island has much less dense forest and more open plains than the North Island. It also has a lot of steep cliffs and mountains. A large river runs through the Southern Island.
There are no story missions on the Southern Island initially, and the island is inaccessible until after the mission Fly South.
- It is unofficially known as South Rook Island, as it is never revealed in-game whether the island actually has a name. However it is possible that it is simply called South Rook Island and along with its northern countpart, North Rook Island, makes up the Rook Islands.