Jefferson Island

Jefferson Island is the island where the entirety of MadWorld is set.

Topography
Being an island, Jefferson Island is surrounded by a not further specified body of water. There are eight bridges that connect it with either the mainland and/or other islands. Prior to the events of MadWorld, the majority of the population seemed to live on the western half of the island, as the districts of Varrigan City, Asian Town and Casino Land are situated on that side of the island. The eastern half of the island seems to be less populated. It has two districts: Mad Castle and Area 66. The Mad Castle area is named after the very large castle that is situated there and leaves little room for habitable space. And as Area 66 is a secret military base and research facility, it is obvious that only a few selected people live there.

Involvement in the DeathWatch games
A few days prior to the events of MadWorld, the entire population of Jefferon Island - save for a few wealthy people - has been taken hostage by a terrorist group. They severed all connection to the outside world by destroying all rail and road access to and from the island, while also disabling the internet connection and jamming phone and satellite signals. They then released an lethal, airborne virus with a maximum incubation time of 24 hours, and promised the cure to anyone that participates in DeathWatch.

Trivia

 * Judging by the presence of Area 66 and Casino Land, which are analogous to Area 51 and Las Vegas, Jefferson Island might be located in the MadWorld universe's equivalent of Nevada, given that the latter two locations are located in that state.