New Jersey

 was a state of the United States of America in which Union City (COMIC: Spiral Staircase) and the city of Trenton could be found. (TV: The Stones of Blood)

It was "just across the water" from New York City. The Staten Island Ferry allowed passage across to New York State. (AUDIO: Invaders from Mars)

Rex Matheson once compared Wales to New Jersey, because it was separated from England by the Severn Bridge, similar to the way New Jersey was separated from New York by bridges. (TV: The New World)

History
In the early 2000s, Major C Jones and several UNIT personnel died in the "Jersey Tollgate Situation". (PROSE: UNIT's New York Operation Expansion)

Dorothy Bell, whilst merged with a quantum harvester, decided to create more bridges to link New York City to New Jersey sometime in the 2010s. Gabby Gonzalez noted that the New Yorkers would hate it. (COMIC: The Fountains of Forever)

Legacy
A human colony planet was named New Jersey. (PROSE: Ten Little Aliens)

Behind the scenes

 * A map of the United States shown in the episode Dalek, set in the then future year of 2012 notably shows New Jersey, Delaware, and Maryland as one state.

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