Liberty (also known as Liberty State or "Liberty City State" on license plates) is an American state in the Grand Theft Auto series. It is the in-game counterpart for the real State of New York. Like New York State, Liberty State is on the east coast of The United States.
Known cities and areas in Liberty State
In GTA 1, there is a landmass to the west of Liberty City known as New Guernsey. This is based on New Jersey, a state that neighbors New York. It is unknown if it's a separate city in-game or just a section of Liberty City.
In GTA IV, there is also a landmass west of Algonquin, which is known as the State of Alderney, which is also based on part of New Jersey.